GIFT   OF 


7 


School 


THE  FLYER'S  GUIDE 


THE 

FLYER'S  GUIDE 

AN  ELEMENTARY  HANDBOOK 
FOR  AVIATORS 


BY 

CAPTAIN  N.  J.  GILL 

ROYAL   ARTILLERY 


NEW  YORK 
E.  P.  BUTTON  AND  COMPANY 

681  FIFTH  AVENUE 


° 


PUBLISHED  1917 
BY  E.  P.  DUTTON  &  CO. 


Printed  in  the  United  States  of  America 


CONTENTS 


CHAPTER  PAGE 

I.  ON  TAKING  A  TICKET  .         »         .       1 
II.  PRACTICAL  FLYING         .         .        ,22 

III.  THE      CONSTRUCTION      OF     AERO- 

PLANES.   THEIR  CARE  AND  MAIN- 
TENANCE  .         .         .         .         .43 

IV.  THE  THEORY  OF  FLIGHT        .         .     74 
V.  INTERNAL  COMBUSTION  ENGINES    .   103 

VI.  IGNITION  DEVICES  135 


398358 


THE  FLYER'S  GUIDE 


CHAPTER  I 

ON  TAKING  A  TICKET 

AEROPLANE  pilots  only  become  proficient 
by  constant  and  untiring  practice.  The  be- 
ginner has  a  long  uphill  fight  before  him,  and 
the  sooner  he  realizes  it  the  better  he  will 
get  on. 

The  first  question  that  arises  in  the  mind 
of  the  would-be  pilot  is  "  on  what  machine 
shaU  I  begin?" 

At  first  the  question  appears  rather  for- 
midable, but  on  more  mature  consideration 
we  can  weed  out  many  of  the  irrelevancies 
that  surround  the  problem.  The  beginner 
naturally  wants  to  learn  on  what  he  calls 
an  "  easy  machine." 

Now  what  is  meant  by  an  easy  machine? 

Obviously  a  machine  upon  which  his  ini- 


2  THE  FLYER'S  GUIDE 

tial  errors  will  have  the  least  effect.  That 
is,  a  machine  which  is  slow  on  its  controls, 
inefficient,  and  with  considerable  reserve  of 
power. 

During  the  early  stages  of  tuition  the 
pupil  is  apt  to  make  exaggerated  movements 
with  the  control  lever;  if  the  machine  is  sen- 
sitive on  its  controls,  such  movements  will 
have  instant  effects  such  as  may  reasonably 
be  expected  to  cause  disquietude  of  mind. 
An  inefficient  machine  may  be  described  as 
being  slow,  with  a  steep,  gliding  angle;  in 
consequence,  the  heavy-handed  push  given 
to  the  control  lever  on  commencing  a  descent 
will  not  cause  the  wires  to  whistle. 

A  considerable  reserve  of  power  will  af- 
ford a  margin  of  safety  to  the  beginner  who 
tries  to  climb  too  steeply. 

Every  beginner  is  bound  to  meet  the  same 
difficulty — namely,  inexperience. 

It  is  the  novelty  of  a  sensation,  hitherto 
untried,  a  certain  feeling  of  elation  and  un- 
easiness, and,  in  most  cases,  sheer  ignorance 
that  are  responsible  for  the  learner's  erratic 
movements. 


ON  TAKING  A  TICKET  3 

Total  ignorance  as  to  the  whole  theory  of 
dynamic  flight  and  its  limitations  can  to  a 
large  measure  be  overcome  by  reading.  This 
I  would  strongly  recommend.  However,  the 
novelty  and  its  effect  on  the  mind  can  only 
be  overcome  by  actually  going  up,  while 
knowledge  gained  on  the  ground  will  require 
to  be  amplified  by  practice. 

It  is  almost  a  natural  instinct  to  move  the 
controls  the  right  way,  given  normal  cir- 
cumstances. The  beginner's  chief  mistake  is 
that  he  moves  them  too  much  and,  where 
landing  is  concerned,  generally  at  not  quite 
the  correct  moment.  It  is  thus  of  the  ut- 
most importance  that  the  pupil  should  essay 
his  first  landings  on  a  slow  machine,  because 
the  ill  effects  of  his  inaccurately  timed  move- 
ments will  be  minimised. 

The  novelty  of  being  in  the  air  entails  a 
certain  loss  of  the  sense  of  feel,  and  beginners 
experience  considerable  difficulty  in  knowing 
whether  the  machine  is  level,  especially  in 
a  fore  and  aft  direction.  The  result  is  an 
undoubted  tendency  to  climb  too  steeply, 
which  is  often  accompanied  by  an  attempt 


4  THE  FLYER'S  GUIDE 

to  turn.  A  little  reserve  of  power  may  then 
save  disaster. 

The  conclusion  may  now  be  drawn  that 
the  pupil  should  commence  his  career  on  a 
slow  but  fairly  powerful  pusher  biplane,  al- 
though more  than  one  tractor  machine  fulfils 
the  above  conditions.  However,  the  tractor 
machine  never  allows  of  the  same  good  view 
being  obtained,  and  creates  a  slip  stream 
which  may  disconcert  the  novice. 

Until  recently  the  box  kite  has  been  the 
favourite  school  machine.  A  50  Gnome  box 
kite,  while  undoubtedly  possessing  many  vir- 
tues, does  not  possess  any  reserve  of  power; 
for  that  reason  I  am  inclined  to  the  opinion 
that  they  are  more  dangerous  than  a  learner's 
machine  need  be. 

No  one  will  deny  that  many  of  our  finest 
pilots  started  on  a  box  kite,  but  such  men 
would  be  equally  good  flyers  on  whatever 
they  had  learnt.  Further,  no  one  will  deny 
that  the  box  kite  has  played  a  very  important 
role  in  the  development  of  aviation. 

In  the  pre-war  days  there  was  not  the 
same  hurry  and  recognised  need  for  pilots, 


ON  TAKING  A  TICKET  3 

so  that  tuition  was  perhaps  more  thorough; 
the  would-be  pilot  was  given  plenty  of  time 
behind  his  instructor  to  learn  the  vicissitudes 
of  the  animal  before  making  his  first  solo. 
Nowadays  a  man  is  expected  to  get  his 
"  ticket "  in  three  or  four  days,  so  it  would 
seem  inevitable  for  the  old  school  box  kite 
to  be  replaced  by  a  somewhat  more  powerful 
machine. 

Without  mentioning  any  type  by  name, 
the  learner  should  have  no  great  difficulty 
in  selecting  a  machine  to  fulfil  the  above 
conditions. 

We  will  now  come  a  step  further  and  con- 
sider the  actual  methods  of  instruction. 

"  Dual  Control  "  is  almost  universally  con- 
sidered to  be  the  quickest  and  most  satis- 
factory way  of  learning — that  is  to  say,  on 
a  machine  fitted  with  two  control  levers  and 
two  rudder  bars,  the  instructor,  however, 
having  sole  control  over  the  engine. 

The  pupil  is  then  taken  up  and  at  once 
allowed  to  control  the  machine  in  the  air, 
any  erratic  movements  being  corrected  by 
the  instructor.  In  this  connection  I  may  say 


6  THE  FLYER'S  GUIDE 

that  the  controls  of  an  aeroplane  are  very 
light,  any  correcting  movement  by  the  in- 
structor being  easily  felt. 

When  the  pupil  begins  to  "  find  his  feet " 
in  the  air,  he  is  allowed  to  try  landings,  the 
pilot  always  having  sole  control  of  the  en- 
gine. 

Pupils  must  try  and  remember  at  all 
times  to  hold  the  control  lightly.  With  an 
absolute  beginner  on  dual  control  this,  is 
essential,  as  it  is  a  bad  thing  to  wear  out 
the  pilot's  strength,  especially  in  the  early 
hours  of  the  morning!  In  addition  it  may, 
of  course,  prove  really  dangerous  if  the  pilot's 
control  is  hampered. 

The  pupil  must  have  engraved  on  his  mind 
the  fact  that  a  machine  only  flies  by  virtue 
of  the  speed  with  which  it  is  passing  through 
the  air.  If  he  allows  that  speed  to  be  lost 
it  will  cease  to  fly. 

The  aviator  of  to-day  is  usually  assisted 
by  various  instruments,  but  opinion  differs 
as  to  the  wisdom  of  allowing  the  learner  to 
use  them.  The  instruments  more  generally 
fitted  are: 


ON  TAKING  A  TICKET  7 

(1)  Some  form   of   air-speed   indicator, 

such  as  a  Pitot  tube; 

(2)  Aneroid  barometer; 

(3)  Revolution  counter; 

(4)  Inclinometer; 

(5)  Watch; 

(6)  Compass. 

(1)  Air-speed  indicators  are  recognised  as 
not  being  dead  accurate,  but  they  should  give 
a  constant  reading  for  any  one  machine. 
They  are  then  manifestly  a  great  help  to 
the  beginner.  He  is  told  that  if  the  indicator 
registers  x  miles  an  hour  the  machine  will 
necessarily  be  in  the  correct  flying  attitude. 
He  is  also  told  at  what  speed  he  should  glide 
and  land. 

It  is  argued,  probably  with  a  certain  amount 
of  truth,  that  such  methods  of  tuition  tend 
to  glue  the  beginner's  eyes  too  much  on  his 
indicator,  with  the  result  that  he  does  not 
acquire  that  great  sense  of  feel,  which  is 
the  mark  of  the  really  first-class  pilot. 

On  the  other  hand,  it  does  undoubtedly 
prove  a  check  to  the  erratic  notions  of  a 


8  THE  FLYER'S  GUIDE 

heavy-handed    beginner.     In    that    way    it 
probably  tends  to  hasten  a  man's  tuition. 

(2)  The  aneroid  barometer  is,  I  think,  with- 
out doubt,  a  very  useful  accessory.    It  is 
harmless,  as  it  is  not  a  direct  help  to  the 
flying  of  a  machine.    Furthermore,  there  is 
in  every  pilot's  mind,  especially  in  the  be- 
ginner's, an  unexplainable  desire,  one  might 
even  say  craving,  to  know  how  high  he  is. 
The  satisfying  of  this  desire  is  a  source  of 
great  encouragement  to  the  novice. 

(3)  A  revolution  counter  is  a  great  safe- 
guard, and  if  used  in  moderation  may  prove 
of  real  assistance  in  learning  how  one's  en- 
gine is  running. 

The  true  habits  of  an  engine  cannot  be 
acquired  in  a  day,  or  even  a  month,  and  a 
judicious  use  of  the  revolution  counter  should 
prove  a  fruitful  source  of  knowledge. 

Before  making  a  flight  the  engine  should 
always  be  run  on  the  ground,  and  the  revo- 
lution counter  will  say  whether  it  is  going 
well  enough  to  attempt  a  flight  or  not. 

Such  an  instrument  should,  I  think,  be 
fitted  to  all  school  machines. 


Not  tc 


ON  TAKING  A  TICKET  9 

(4)  The  inclinometer  is  a  spirit  level  marked 
in  degrees  to  show  at  what  angle  the  ma- 
chine is  to  the  horizon  in  a  lateral  sense.    As 
a  rule  they  are  rather  inclined  to  stick,  and 
are  of  little  value  to  the  beginner. 

(5)  A  watch  is  a  decided  source  of  comfort. 

(6)  Compass.    Not    necessary    for    aero- 
drome tuition. 

To  sum  up,  my  opinion  is  that  a  school 
machine  should  be  fitted  with: 

(1)  Aneroid  barometer; 

(2)  Revolution  counter; 

(3)  Watch. 

All  instruments  are  liable  to  go  wrong, 
and  it  is  a  bad  principle  to  allow  the  pupil 
to  put  his  entire  faith  in  them. 

To  go  back  to  our  beginner.  He  continues 
his  practice  from  the  passenger's  seat  until 
his  instructor  considers  that  he  is  compe- 
tent to  control  the  machine  in  calm  air  and 
land  himself.  During  the  instructional  flights 
it  is  of  the  utmost  importance  that  a  great 
number  of  landings  be  made,  and  the  in- 
structor must  be  satisfied  of  the  pupil's 
ability  to  land  before  allowing  him  to  go  solo. 


10  THE  FLYER'S  GUIDE 

The  first  solo  flight  will  be  short,  and  the 
beginner  should  continue  such  practice  for 
some  hours  over  the  aerodrome,  in  order  to 
make  certain  of  his  ability  to  effect  a  tolerably 
good  landing  under  normal  conditions.  Dur- 
ing these  flights  the  pupil  must  be  careful  to 
keep  within  reach  of  the  aerodrome.  He  will 
then  combine  landing  practice  with  elementary 
air  experience,  such  as  making  wide  turns,  etc. 

Instructors  must  be  very  careful  to  as- 
certain that  each  pupil  is  thoroughly  acquaint- 
ed with  the  details  of  the  controls  before 
allowing  the  latter  to  start  off  on  a  solo. 

In  all  aerodromes  there  are  rules  as  to 
which  way  machines  should  go  around  and 
land  according  to  the  wind.  These  must  be 
thoroughly  explained  to  the  pupil  before 
sending  him  up.  He  should  also  be  acquainted 
with  the  Royal  Aero  Club's  rules  on  aerial 
navigation. 

The  beginner  should  be  disabused  of  the 
old  fallacy  as  to  the  colossal  difficulty  of  a 
right-hand  turn. 

It  is  admitted  that  with  ill-balanced,  badly 
trued  box  kites  a  right-hand  turn  was  "  some  " 


ON  TAKING  A  TICKET  11 

undertaking.  In  the  type  of  school  machine 
now  under  discussion  the  beginner  should  be 
clearly  told  that  there  is  no  difference  be- 
tween a  left  and  right-handed  turn. 

Having  learnt  how  to  put  the  machine 
on  the  ground  without  breaking  it  and  in  a 
reasonable  manner,  our  novice  must  next 
practice  landing  on  a  mark. 

To  land  reasonably  near  any  mark  from 
an  appreciable  height  requires  practice,  which 
must  be  given  with  a  generous  hand.  It 
should  not,  however,  take  very  long  for  our 
budding  aviator  to  make  certain  that  he  can 
land  within  50  yards  of  a  given  mark  from 
some  300  feet.  He  should  then  be  made  to 
do  a  series  of  vol-planes  from  400  or  500 
feet  with  his  engine  completely  shut  off. 

He  is  then  ready  to  take  his  Royal  Aero 
Club's  brevet. 

The  tests  for  this  brevet  are  two  series  of 
five  figures  of  eight  each  round  two  given 
marks.  At  the  end  of  each  series  a  landing 
has  to  be  made  withing  50  yards  of  a  given 
mark.  In  addition,  a  third  flight  has  to  be 
made  to  a  height  of  not  less  than  about  400 


12  THE  FLYER'S  GUIDE 

feet  and  a  descent  effected  with  the  engine 
completely  cut  off. 

Many  people  only  take  about  three  or  four 
hours'  actual  flying  before  they  take  their 
tickets.  That  is  certainly  quick,  but  I  think 
a  good  ticket  should  be  taken  after  six  or 
seven  hours  in  the  air. 

It  must  be  clear  then  that  a  so-called  certi- 
fied pilot  and  no  more  has  but  very  little 
experience.  All  beginners  will  do  well  to 
realise  this  and  appreciate  that  they  have 
only  just  begun. 

A  boy  who  has  just  taken  his  ticket  is 
naturally  very  pleased  with  himself,  and 
thinks  there  is  nothing  about  aviation  that 
he  does  not  know.  It  is  a  great  mistake 
and  sometimes,  alas,  a  fatal  one.  Always 
remember  in  aviation  that  you  learnt  to 
walk  before  you  could  run. 

Under  existing  conditions  the  pressing  need 
for  pilots  has  led  to  the  suspension  of  the 
formality  of  military  pilots  having  to  take 
the  Royal  Aero  Club's  brevet.  Elementary 
instructions,  corresponding  to  the  standard 
required  to  pass  the  above  tests,  is,  however, 


ON  TAKING  A  TICKET  13 

imparted  to  all  pupils  before  they  are  sent 
on  to  learn  machines  whose  performances 
more  nearly  approximate  those  of  present- 
day  service  machines. 

It  may  be  appropriate  to  add  a  few  words 
with  regard  to  clothing.  There  are  such  a 
large  number  of  disguises  on  the  market 
that  the  intending  aviator  may  experience 
some  difficulty  in  making  his  choice. 

Unless  the  pilot  is  comfortable  in  his 
machine,  he  will  become  fidgety,  and  his 
attention  will  be  slightly  disturbed.  To  be 
comfortable  then  is  a  necessity.  Comfort  can 
only  be  attained  by  being  properly  clothed. 
Even  in  summer  and  at  a  few  hundred  feet 
only  it  is  rather  cold  work  sitting  still  in  an 
aeroplane,  while  in  winter  the  cold  becomes 
really  acute. 

A  warm  coat  should  always  be  worn.  Not 
necessarily  leather,  but  something  in  which 
one's  movements  are  free  and  easy.  Leather, 
of  course,  is  a  special  advantage  in  certain 
tractor  machines  where  oil  is  flowing  freely. 

The  hands  and  feet  are  perhaps  the  easiest 
target  for  the  cold,  so  that  particular  care 


14  THE  FLYER'S  GUIDE 

should  be  devoted  to  obtaining  a  really  com- 
fortable warm  pair  of  gloves. 

Leather  gauntlet  gloves,  with  some  form 
of  woollen  lining,  would  appear  the  most 
satisfactory;  but  the  leather  should  be  suf- 
ficiently soft  to  allow  the  fingers  and  wrists 
to  move  freely.  Whatever  the  pattern  se- 
lected it  is  essential  that .  gloves  shall  be 
sufficiently  large  without  being  clumsy. 

Warm  socks  or  stockings  are  essential  to 
keep  the  feet  warm.  A  great  many  pilots 
like  to  fly  in,  gun  boots.  But  here  again 
the  same  principle  applies.  Something  warm, 
sufficiently  large  to  be  comfortable,  without 
being  too  large  to  fit  on  the  rudder  bar. 

The  head  and  ears  require  protection,  which 
is  best  afforded  by  a  woollen  or  leather 
(wool  lined)  cap. 

If  no  wind  screen  is  provided,  goggles 
must  be  worn.  This  is  important.  At  first 
you  may  find  that  your  eyes  get  used  to  the 
rush  of  air  and  do  not  water.  However,  the 
perpetual  strain  on  the  eyes  is  bound  to  tell, 
and  trouble  will  ensue.  If  you  are  lucky 
enough  to  have  strong  eyes  and  a  good  sight, 


ON  TAKING  A  TICKET  15 

remember  they  were  given  to  you  to  use 
and  not  to  abuse. 

If  flying  a  tractor  machine  whose  engine 
throws  back  much  oil,  take  a  small  piece  of 
chamois  leather  with  which  to  wipe  your 
goggles.  It  is  no  use  smearing  the  glass 
with  gloves  or  a  handkerchief;  it  only  makes 
matters  worse.  In  most  machines  of  to-day 
efficient  wind  screens  are  provided  which  do 
away  with  the  necessity  of  goggles. 

When  in  the  machine,  get  settled  comfort- 
ably in  the  seat  and  use  a  deep  safety-belt 
with  quick  release.  See  that  the  belt  is 
correctly  adjusted  for  your  particular  ro- 
tundity; it  should  be  tight  enough  to  pre- 
vent your  falling  forward  in  the  unhappy 
event  of  an  abrupt  landing. 

With  regard  to  the  actual  flying  of  a  machine 
there  is  little  to  be  said,  as  it  can  only  be 
acquired  by  practice.  I  am,  however,  tempted 
into  writing  a  few  paragraphs  for  the  benefit 
of  those  quite  uninitiated. 

It  is  necessary  before  attempting  a  solo 
flight  to  learn  to  control  the  machine  on  the 
ground.  An  aeroplane  is  steered  by  means 


16  THE  FLYER'S  GUIDE 

of  a  rudder,  which  is  connected  to  a  rudder 
bar  worked  by  the  pilot's  feet.  Now  the 
rudder  is  designed  to  steer  the  machine  in 
normal  flight — that  is  to  say,  when  the 
machine  is  passing  through  the  air  at  a  high 
speed;  therefore,  when  the  machine  is  travel- 
ling slowly  on  the  ground,  there  will  be  very 
little  wind  pressure  and  the  rudder  will  not 
have  very  much  effect.  In  consequence, 
until  the  machine  has  nearly  attained  flying 
speed,  it  will  be  found  difficult  to  steer. 
Once  the  tail  is  in  the  air,  flying  speed  being 
almost  reached,  it  will  be  found  to  answer 
the  rudder  very  quickly. 

When  "  taxying  "  with  the  tail  down,  big 
movements  of  the  rudder  will  be  found  neces- 
sary; but,  when  flying,  a  small  movement  is 
sufficient  to  commence  a  turn. 

Care  must  be  taken  not  to  turn  the  ma- 
chine quickly  on  the  ground  when  travelling 
fast,  because  the  sudden  change  of  direction 
will  probably  remove  the  undercarriage.  A 
machine  can  be  turned  when  travelling  very 
slowly  on  the  ground  by  opening  the  engine 
out  for  a  moment  or  two  and  then  cutting 


ON  TAKING  A  TICKET  17 

it  off  again.  This  momentary  acceleration 
of  the  propeller  will  not  be  sufficient  to  start 
the  machine  travelling  fast,  but  the  resultant 
slip  stream  will  create  a  large  pressure  on 
the  rudder  if  held  well  over. 

The  fore  and  aft  control  is  effected  by 
means  of  a  hinged  elevator  flap,  which  is 
worked  from  the  pilot's  seat  by  means  of 
a  lever.  As  the  lever  is  pushed  forward  the 
elevator  is  depressed,  thus  offering  a  surface 
to  the  wind  stream.  The  pressure  on  this 
surface  causes  the  tail  to  rise.  When  the 
elevator  is  straight  out  behind — i.e.,  hori- 
zontal— there  is  no  pressure  on  it,  and, 
when  pulled  up  above  the  horizontal,  the 
pressure  on  it  causes  the  tail  to  drop. 

To  revert  to  our  pupil,  let  us  imagine  him 
starting  off  for  a  flight.  In  a  good  aerodrome 
he  will  always  be  able  to  start  dead  into  the 
wind  and  be  able  to  keep  over  possible  land- 
ing-ground until  high  enough  to  turn  with 
safety.  As  a  matter  of  fact,  a  beginner  should 
only  be  allowed  out  in  calm  weather;  but, 
however  light  the  wind,  he  should  be  made 
to  start  dead  into  it. 


18  THE  FLYER'S  GUIDE 

We  assume  then  that  he  starts  from  the 
sheds  dead  into  the  wind.  He  will  push 
the  control  lever  forward  until  the  tail  gets 
well  in  the  air  and  the  machine  assumes  a 
horizontal  or  flying  position.  As  the  speed 
increases  the  control  lever  will  have  to  be 
pulled  gently  back  until  the  machine  attains 
its  flying  speed.  The  control  lever  will  then 
be  held  steady,  and,  after  running  along  the 
ground  for  some  distance  (varying  from  about 
70  to  300  yards  according  to  the  machine), 
the  machine  will  gradually  lift.  Most  ma- 
chines will  climb  while  in  the  horizontal 
flying  position  when  the  engine  is  full  on, 
so  that  our  pupil  will  not  require  to  pull  the 
lever  back  at  all.  Great  care  must  be  taken 
not  to  let  the  machine  get  at  a  steep  angle. 

When  about  200  feet  a  wide  turn  may  be 
attempted.  Press  the  rudder  gently,  and 
at  the  same  time  push  the  control  lever 
slightly  forward  to  ensure  that  the  machine 
is  not  climbing.  Some  machines,  however, 
tend  to  dive  themselves  on  a  right-hand  turn 
and  climb  on  a  left-hand  one,  and  vice  versa. 

However,  on  an  ordinary  slow  pusher  with 


ON  TAKING  A  TICKET  19 

fixed  engine  (that  is,  non-rotary)  the  be- 
ginner will  not  be  worried  with  any  antics 
of  that  kind.  He  will  just  have  to  take  care 
that  he  does  not  lose  flying  speed,  while  being 
equally  careful  not  to  get  into  a  nose  dive. 
The  machine  should,  in  fact,  be  flying  al- 
most horizontally  (if  anything  very  slightly 
downwards). 

The  method  of  lateral  control  is  explained 
in  a  later  chapter,  but,  briefly,  the  principle 
is  this.  The  incidence  of  the  plane  (or  planes) 
on  one  side  is  increased  while  that  on  the 
other  is  decreased,  and  vice  versa. 

By  increasing  the  incidence  on  one  side, 
the  lift  is  increased  on  that  side  and  decreased 
on  the  other.  So  to  bank  a  machine  for  a 
left-hand  turn  the  control  lever  is  held  over 
to  the  left,  which  has  the  effect  of  decreasing 
the  incidence  on  the  left  plane  while  in- 
creasing that  on  the  right.  The  left-hand 
plane  then  tends  to  drop  and  the  right-hand 
one  to  rise. 

Similarly,  if  a  gust  of  wind  causes  an 
increased  lift  on  the  left-hand  plane  it  is  cor- 
rected by  moving  the  control  lever  to  the  left. 


20  THE  FLYER'S  GUIDE 

The  actual  methods  of  effecting  this  lateral 
control  are: 

(1)  By  means   of    flaps    (called   ailerons) 

hinged    to    the    rear    spar    of    the 
planes;  or 

(2)  By  warping  the  rear  spar  of  the  planes. 

These  two  methods  are  described  in  greater 
detail  in  Chapter  III. 

Many  machines  bank  themselves  quite  ap- 
preciably on  a  turn,  so  that  the  beginner 
will  only  have  to  assist  very  slightly  with  the 
warp  on  his  first  wide  turns.  He  should, 
however,  get  into  the  way  at  once  of  turning 
with  a  slight  bank.  If  no  bank  is  applied, 
the  machine  will  slip  outwards,  which  is 
very  ungraceful  and  may  even  prove  a  source 
of  danger. 

The  first  descents  should  always  be  straight 
glides.  The  pupil  must  get  his  machine 
facing  direct  into  the  wind  (that  is  the  way 
he  will  land)  before  shutting  off  the  engine. 

Whatever  the  machine,  it  should  be  glided 
at  a  speed  just  lower  than  its  normal  flying 
speed.  Great  care  must  of  course  be  exer- 


ON  TAKING  A  TICKET  21 

cised  not  to  stall  it,  but  the  happy  mean 
should  become  a  second  nature  with  practice. 
The  actual  landing  must  be  made  at  a  greatly 
reduced  speed.  To  this  effect  the  control 
lever  should  be  pulled  very  slowly  back  when 
about  10  feet  off  the  ground.  A  perfect 
landing  would  be  such  that  the  wheels  and 
tail  skid,  touch  the  ground  together,  but  the 
beginner  should  not  attempt  such  an  ideal 
at  first.  He  would  be  almost  certain  to  mis- 
judge his  height,  "  pancake,"  rather  severely, 
with  probable  damage  to  the  undercarriage. 

Landing  is  an  operation  that  requires  great 
care  and  attention,  it  being  necessary,  es- 
pecially in  the  vicinity  of  aerodromes,  to  keep 
a  sharp  lookout  for  the  movements  of  other 
machines.  It  is  never  advisable  to  purposely 
lose  one's  engine  when  gliding,  as  it  may 
suddenly  be  required  to  avoid  a  collision, 
or  even  to  neutralise  the  effects  of  an  ill- 
judged  landing. 


CHAPTER  II 

PRACTICAL   FLYING 

AERONAUTICS  being  at  present  entirely  sub- 
servient to  military  requirements,  it  may  not 
be  amiss  to  consider  the  practical  side  of 
flying  from  a  purely  military  point  of  view. 

The  object  of  military  aviation  is  two-fold: 

(a)  To  gain  intelligence; 

(6)  Offensive  action,  such  as  bomb-drop- 
ping. 

To  carry  out  these  missions,  fighting  ma- 
chines are  a  necessary  adjunct;  so  without 
going  further  into  the  subject  it  is  obvious 
that  the  practical  pilot  must  be  an  experi- 
enced cross-country  flyer. 

It  is  with  the  object  of  giving  a  few  hints 
about  cross-country  flying  that  these  para- 
graphs are  written. 

Considerable  aerodrome  practice  is  neces- 
sary after  taking  a  ticket  before  making  a 
cross-country  flight.  The  limited  scope  of 

22 


PRACTICAL  FLYING  23 

elementary  training  was  clearly  indicated  in 
the  foregoing  chapter.  On  an  average  the 
newly  certified  aviator  has  not  been  higher 
than  some  500  feet,  and  then  only  in  the 
calmest  weather.  It  is  then  essential  that 
he  should  put  in  several  hours  on  the  same 
or  a  similar  type  of  machine  in  short  flights 
over  the  aerodrome.  Each  time  he  should  go  a 
little  higher,  until  he  gets  quite  used  to  being 
at  2000  or  3000  feet.  Once  he  is  used  to 
that  height,  he  will  not  find  that  greater 
altitudes  in  any  way  worry  him. 

Every  flight  should  be  terminated  by  a 
practice  landing  on  some  particular  mark. 
As  the  pilot  becomes  more  proficient  and 
self-confident,  he  should  practise  turning  while 
vol-planing.  At  first  the  turns  should  be 
very  wide  and  not  through  more  than  180 
degrees  (that  is  half  a  turn).  Keep  the  ma- 
chine at  its  normal  gliding  angle  throughout 
the  turn.  At  first  the  tendency  of  the  be- 
ginner will  probably  be  towards  rather  a  steep 
descent. 

This  malpractice  must  be  overcome  before 
attempting  a  complete  turn.  By  degrees  the 


24  THE  FLYER'S  GUIDE 

turns  can  be  made  smaller  until  a  neat  spiral 
of  about  2|  turns  be  accomplished  in  1000 
feet. 

By  dint  of  constant  practice  the  art  of 
turning  sharply  and  effecting  steeply  banked 
spirals  is  gradually  acquired,  but  care  must 
be  taken  not  to  attempt  aerial  acrobatics 
at  an  height  of  less  than  about  1000  feet  above 
the  ground. 

Some  eight  or  ten  hours  of  such  aerodrome 
practice  should  render  the  average  pupil  suf- 
ficiently skilled  to  undertake  a  short  cross- 
country flight. 

His  first  expedition  across  country  should 
be  round  some  well-defined  objectives  in  the 
vicinity  of  the  aerodrome,  and  should  not 
last  more  than  half  an  hour  or  forty  minutes. 
A  few  short  flights  of  this  nature  will  tend 
to  create  confidence  and  inspire  enthusiasm, 
whilst  affording  the  pupil  occasion  to  accus- 
tom himself  to  beholding  mother  earth  from 
above.  From  a  gradual  "  air-seasoning  "  of 
this  kind  the  pupil  will  eventually  learn  to 
anticipate  the  country  that  lies  before  him 
by  a  careful  study  of  the  map. 


PRACTICAL  FLYING  25 

Before  making  long  flights  in  any  weather, 
experience  must  be  obtained  over  short  courses 
on  selected  days. 

Similarly,  before  taking  a  new  machine 
across  country,  considerable  practice  must  be 
obtained  over  an  aerodrome.  A  few  landings 
hi  adjoining  fields,  where  practicable,  should 
prove  of  real  value. 

In  the  previous  chapter  the  use  of  the 
following  instruments  was  advocated  on  be- 
half of  the  beginner  in  his  initial  struggles: 

(1)  Aneroid  barometer; 

(2)  Revolution  counter; 

(3)  Watch. 

For  cross-country  work  the  following  should 
be  added: 

(4)  Compass; 

(5)  Air-speed  indicator; 

(6)  Inclinometer. 

Although  few  pilots  rely  on  the  compass 
to  find  their  way,  it  is  of  the  greatest  use 
under  certain  circumstances. 

It  is  always  advisable  to  look  up  one's 
course  on  a  map  before  starting  off  and  to 


26  THE  FLYER'S  GUIDE 

note  down  the  compass  bearing  from  point 
to  point.  These  bearings  should  be  marked 
on  the  map  or  a  separate  piece  of  paper  so 
that  they  are  clearly  visible  from  the  pilot's 
seat. 

The  compass  bearing  then  forms  a  check 
if  the  pilot  is  following  a  railway,  canal,  etc., 
on  the  ground.  Many  pilots  have  lost  their 
way  through  following  the  wrong  railway,  etc. 
Such  errors  might  be  avoided  by  a  judicious 
use  of  the  compass.  A  still  stronger  raison 
d'etre  exists  for  the  compass  when  flying  over 
the  sea  or  in  clouds.  In  either  of  these  cases 
a  compass  is  essential,  as  it  then  forms  the 
sole  means  of  finding  one's  way. 

There  are  two  sources  of  error  peculiar 
to  the  compass.  They  are: 

(1)  Variation; 

(2)  Deviation. 

By  variation  is  meant  the  angle  between 
true  north  and  magnetic  north.  The  varia- 
tion is  different  for  every  place,  and  changes 
from  year  to  year.  At  present  the  variation 
in  London  is  about  16°  W.  That  is  to  say, 


PRACTICAL  FLYING  27 

the  compass  points  16°  W.  of  true  north. 
It  is  important  to  remember  this  when 
taking  a  course  from  a  map,  because  maps 
are  made  in  relation  to  true  north.  To  take 
an  example.  Suppose  a  course  on  the  map 
is  due  east,  that  is  to  say  90°  over  an  area 
where  the  variation  is  about  17°  West.  The 
compass  course  would  then  be  90° +  17°, 
that  is,  107°. 

Deviation  is  an  error  caused  by  the  prox- 
imity of  metal  to  the  compass.  The  large 
amount  of  metal  work  hi  an  aeroplane  will 
thus  cause  a  big  deviation.  It  is  quite  im- 
possible to  lay  down  any  rules  about  devia- 
tion. It  is  different  in  every  machine,  and 
even  varies  for  every  position  of  the  com- 
pass in  any  one  machine. 

It  is  corrected,  as  far  as  possible,  by  placing 
small  magnets  under  the  compass  approxi- 
mately at  right  angles  to  the  north  and  south 
line.  When  this  adjustment  is  being  car- 
ried out,  the  areoplane  should  be  placed  in 
the  middle  of  a  field  as  far  from  any  metal 
(such  as  iron  palings,  etc.)  as  possible.  It 
is  even  advisable  to  do  it  with  the  engine 


28  THE  FLYER'S  GUIDE 

running,  as  the  magneto  being  then  in  action 
may  materially  affect  the  deviation. 

It  is  not  intended  to  describe  this  adjust- 
ment (or  compass  swinging,  as  it  is  called) 
in  detail,  as  it  hardly  comes  within  the  scope 
of  this  work. 

The  air-speed  indicator  was  discussed  in 
the  previous  chapter,  and  I  ventured  the 
opinion  that  it  should  not  be  used  by  begin- 
ners in  the  first  stage.  For  long-distance 
flights  in  any  weather  it  is,  however,  a  great 
asset.  The  cross-country  pilot  will  be  con- 
tinually flying  in  or  through  clouds.  It  is 
in  such  circumstances  that  an  air-speed  indi- 
cator becomes  an  urgent  need.  Imagine  a 
pilot  in  a  cloud.  He  cannot  see  the  ground; 
he  can  see  nothing  but  the  damp  obscurity 
that  surrounds  him.  He  inevitably  loses  all 
sense  of  speed  and  direction,  unconsciously 
allowing  the  machine  to  assume  the  most 
alarming  attitudes.  How  many  pilots,  on 
emerging  from  a  cloud,  have  been  horrified 
to  find  themselves  in  a  steep  nose  dive! 

Such  incidents  can  be  avoided  by  the  use 
of  certain  instruments. 


PRACTICAL  FLYING  29 

The  compass,  as  already  explained,  pro- 
vides the  necessary  assurance  with  regard 
to  direction.  By  means  of  an  air-speed  in- 
dicator the  pilot  can  keep  his  machine  in 
the  normal  position  fore  and  aft.  Similarly 
an  inclinometer  will  prevent  him  allowing 
the  machine  to  stand  on  a  wing  tip. 

All  instruments  should  be  arranged  care- 
fully in  front  of  the  pilot,  so  that  he  can 
read  them  in  comfort. 

For  night  flying  the  above  instruments  are 
more  than  ever  necessary,  and  they  must  be 
well  illuminated. 

Before  starting  off  across  country,  it  is 
as  well  to  make  certain  that  you  have  enough 
petrol  and  oil  in  your  tanks.  In  addition, 
a  certain  number  of  tools,  a  sparking  plug 
or  two,  some  wire,  etc.,  should  be  carried. 
Your  map,  with  route  clearly  marked,  must 
be  placed  so  that  you  can  read  it  in  com- 
fort. The  engine  must  be  run  on  the  ground 
to  your  entire  satisfaction.  It  is  never  worth 
while  commencing  a  flight  with  an  engine  that  is 
not  doing  its  best.  Get  to  a  reasonable  height 
over  the  aerodrome  before  leaving  its  vicinity. 


30  THE  FLYER'S  GUIDE 

It  is  difficult  to  say  anything  very  definite 
about  the  height  at  which  cross-country 
flights  should  be  made.  It  depends  on  the 
circumstances  of  each  case.  On  service,  for 
instance,  reconnaissances  are  made  at  an 
average  height  of  about  14,000  feet,  at  which 
height  one  may  expect  to  enjoy  comparative 
immunity  from  rifle  fire.  "Archie,"  how- 
ever, is  not  so  easy  to  outclimb,  and  has 
frequently  been  known  to  burst  above  this 
height. 

At  home  I  would  recommend  3000  feet 
as  being  a  comfortable  kind  of  average  for 
cross-country  flying.  In  many  parts  of  the 
country,  where  there  is  an  abundance  of 
good  landing  ground,  it  is  perfectly  safe  to 
come  down  considerably  lower,  perhaps  to 
1500  feet.  Again,  where  the  country  is  par- 
ticularly bad,  it  may  be  advisable  to  fly 
higher,  perhaps  at  5000  feet  or  thereabouts. 

The  point  is  that  you  want  to  be  sufficiently 
high  to  reach  good  ground  in  the  event  of 
engine  failure.  Such  a  height  should  then  give 
time  to  consider  how  the  selected  field  is  to 
be  approached,  having  due  regard  to  the  wind. 


PRACTICAL  FLYING  31 

The  height  at  which  you  select  to  fly  should 
also  be  considerably  dependent  on  the  wind 
and  clouds.  Both  the  direction  and  velocity 
of  the  wind  vary  with  the  height  above  sea- 
level.  The  direction,  as  a  rule,  veers  clock- 
wise from  sea-level  up  to  some  3000  feet, 
after  which  it  appears  to  be  fairly  constant. 
The  velocity  increases  from  sea-level,  be- 
coming a  maximum  at  about  4000  feet, 
above  which  it  would  seem  to  remain  fairly 
steady. 

As  an  example:  a  ground  wind  of  15  m.p.h. 
from  S.W.  would  probably  be  about  30  m.p.h. 
from  W.  at  4000  feet. 

So  if  flying  westwards  on  such  a  day,  the 
higher  you  flew  the  more  would  you  be  im- 
peded by  the  wind.  If  flying  eastwards,  on 
the  other  hand,  the  wind  will  be  of  more 
assistance  the  greater  the  altitude. 

If  the  clouds  are  thick  and  numerous,  one 
of  two  courses  must  be  adopted.  Either  fly 
below  them  if  they  are  sufficiently  high  to 
allow  of  this,  or,  if  they  are  very  low,  it  will 
be  necessary  to  get  above  them  and  fly  en- 
tirely by  compass  bearing.  In  the  latter 


32  THE  FLYER'S  GUIDE 

event  I  would  recommend  a  descent  being 
made  at  regular  intervals  (every  20  miles 
or  so)  until  the  earth  becomes  visible  in  order 
to  verify  one's  position. 

A  few  words  now  with  regard  to  finding 
one's  way. 

It  is  most  necessary  to  have  a  good  map 
of  the  whole  course.  I  personally  think  J" 
Ordnance  Survey  is  the  most  suitable  map 
for  ordinary  cross-country  work.  The  course 
should  be  clearly  marked  and  the  map  ar- 
ranged in  its  case.  Owing  to  limitations  of 
space  and  weight  you  will  find  very  few 
map-cases  more  than  about  9  inches  long. 
This  then  allows  of  about  36  miles  on  the 
map  being  visible  at  any  one  time.  The 
roller  map-case  overcomes  this  difficulty,  as 
a  long  length  of  map  can  be  put  on  the  rollers. 
As  the  pilot  advances  along  his  course  he  can 
keep  pace  on  the  map  by  turning  one  of  the 
rollers. 

Provided  that  the  ground  is  visible,  the 
whole  course  should  be  followed  on  the  map. 
Certain  objects  stand  out  very  clearly,  and 
these  should  always  be  looked  for.  Water 


PRACTICAL  FLYING  33 

is  perhaps  the  best  guide  to  the  aviator. 
Canals,  rivers,  and  reservoirs  prove  of  the 
greatest  assistance.  Railways  too  stand  out 
very  clearly  in  open  country.  Even  hi  en- 
closed country  they  are  usually  to  be  found 
from  the  smoke  of  a  passing  train.  Roads 
are  apt  to  be  rather  deceptive,  especially  hi 
England,  where  there  are  so  few  straight 
stretches;  furthermore,  there  are  many  miles 
of  roads  concealed  by  trees;  also  unimportant 
roads  in  existence  that  are  not  marked  on 
the  map.  Main  roads,  if  they  are  covered 
with  tarmac,  are  not  nearly  so  visible  as 
the  second-class  macadamed  road. 

In  any  flight  that  you  are  likely  to  under- 
take you  are  almost  sure  to  find  either  a 
river,  canal,  or  railway  along  a  greater  part 
of  it.  If  you  do  not  happen  to  have  one 
of  them  to  follow,  you  will  be  continually 
cutting  them,  when  you  can  check  your 
exact  position  on  the  map.  Towns  and  large 
forests,  being  visible  from  a  long  distance, 
are  also  of  great  assistance. 

In  addition,  the  course  should  throughout 
be  checked  by  compass  bearing.  It  is  most 


34  THE  FLYER'S  GUIDE 

necessary  to  make  allowance  for  a  side  (or 
partially  side)  wind  when  using  the  compass. 
For  example,  an  aeroplane  travelling  from 
A  to  B  (B  being  west  of  A),  in  a  northerly 
wind  has  to  steer  considerably  north  of  west 
to  counteract  the  effect  of  the  wind. 

If  the  exact  strength  and  direction  of  the 
wind  were  known  for  the  height  at  which  a 
flight  is  to  be  made,  the  necessary  allowance 
could  easily  be  calculated  from  an  ordinary 
parallelogram  of  forces.  As  the  wind  is  such 
a  variable  quantity,  this  is  not  a  very  prac- 
tical method.  The  best  way  to  make  the 
necessary  allowance  is  as  under: 

Climb  to  the  height  at  which  you  intend 
to  fly,  over  the  aerodrome;  start  exactly  over 
the  aerodrome  in  a  direction  along  your 
course.  There  is  almost  certain  to  be  some 
prominent  object  within  view  along  this 
course;  about  5  miles  would  be  a  suitable 
distance.  Steer  direct  at  this  point  and  note 
the  compass  reading,  which  will  be  the  cor- 
rect one  for  that  course.  On  changing  course 
the  procedure  should  be  repeated. 

Such  a  method  is,  of  course,  only  wholly 


PRACTICAL  FLYING  35 

possible  when  flying  below  the  clouds.  If  a 
flight  is  to  be  made  entirely  above  the  clouds, 
the  necessary  allowance  for  wind  must  be 
calculated.  Meteorological  reports  should 
be  available  at  any  aerodrome,  giving  the 
strength  and  direction  of  the  wind  at  various 
heights.  Failing  this,  the  strength  and  di- 
rection of  the  wind  at  the  ground  level  can 
be  read  from  an  anemometer  and  deduced 
for  any  other  height.  Under  such  circum- 
stances it  is  essential  to  haVe  the  compass 
accurately  adjusted  to  counteract  deviation, 
and  to  make  proper  allowance  for  variation. 

Although  not  advocating  this  method  of 
finding  a  compass  course,  it  should  be  pos- 
sible to  get  within  5  or  10  degrees  of  the 
required  direction.  As  already  explained,  the 
accuracy  of  the  calculation  should  be  tested 
by  a  regular  descent  below  the  clouds. 

I  now  come  on  to  the  rather  thorny  ques- 
tion of  forced  landings.  To  land  a  machine 
where  one  wants  and  in  an  orderly  manner 
is  by  far  the  most  difficult  part  of  flying. 
When  forced  to  descend  across  country,  there 
is  the  further  difficulty  of  determining  where 


36  THE  FLYER'S  GUIDE 

one  does  not  want  to  land.  As  soon  as  the 
engine  stops  it  becomes  necessary  to  choose 
a  landing-place. 

Provided  one  has  a  sufficient  margin  of 
height,  there  is  time  to  look  around  and 
make  a  careful  selection.  There  is  of  neces- 
sity a  great  element  of  uncertainty  when 
choosing  a  ground  from  above. 

It  must  be  borne  in  mind  that  an  aeroplane 
will  only  land  on  certain  surfaces.  The  ordi- 
nary aerodrome  is  grass  covered,  and  short 
grass  does  perhaps  form  the  most  suitable 
surface  possible.  However,  when  forced  to 
descend  in  strange  country,  if  you  decide 
on  a  grass  field,  make  certain  it  is  grass. 
Roots  and  unripe  corn  are  also  green,  and 
at  any  height  are  very  difficult  to  distinguish 
from  grass. 

Then  there  is  grass  and  grass.  Uncut 
hay  presents  the  same  disadvantages  to  the 
aviator  as  corn  does.  It  is  almost  impossible 
to  land  a  machine  in  corn  or  long  grass,  be- 
cause the  wheels  and  skids  (if  any)  will  catch 
in  it  and  cause  the  machine  to  turn  over  its 
nose  on  to  its  back.  It  might  be  possible 


PRACTICAL  FLYING  37 

for  a  very  skilful  pilot  to  land  certain  ma- 
chines in  corn  without  turning  over,  but  the 
landing  would  have  to  be  so  slow  that  the 
machine  had  practically  lost  all  forward  way. 
It  would,  in  fact,  be  a  "pancake"  landing, 
which  would  very  likely  break  the  under- 
carriage. 

If  you  do  find  yourself  about  to  settle  in 
corn,  you  must  of  course  pancake,  the  pos- 
sibility of  a  broken  undercarriage  being  a 
far  lesser  evil  than  a  cartwheel  over  the  nose 
of  the  machine. 

Then  again,  suppose  one  did  effect  a  suc- 
cessful landing  in  crops,  it  would  be  impos- 
sible to  get  out  of  them  without  beating 
down  a  track  for  the  machine  to  run  along. 
Material  damage  of  that  kind  should  always 
be  avoided.  So  from  every  point  of  view 
avoid  landing  in  crops. 

On  a  windy  day  it  should  be  possible  to 
spot  long  grass  or  corn,  as  the  wind  sets  up 
a  wavy  motion. 

In  the  fall  of  the  year,  when  the  corn  has 
been  cut,  stubble  forms  an  excellent  surface. 
Ordinary  plough  is  quite  possible,  but  great 


38  THE  FLYER'S  GUIDE 

care  must  be  taken  to  settle  very  slowly. 
Where  the  furrows  are  more  than  usually 
deep  it  should  be  avoided. 

As  the  surface  of  an  unknown  ground  is  such 
an  uncertain  quantity,  it  is  of  the  first  im- 
portance to  see  that  its  surroundings  make  a 
descent  feasible.  For  instance,  a  ground  sur- 
rounded by  trees  should  be  avoided  unless, 
of  course,  the  available  landing  surface  is 
particularly  large;  it  is  always  most  difficult 
to  alight  successfully  over  trees. 

An  efficient  machine  dived  steeply  on  such 
an  occasion  will  have  acquired  an  enormous 
speed  by  the  time  it  is  flattened  out.  The 
result  will  be  a  collision  with  whatever  there 
happens  to  be  at  the  other  end  of  the  field. 
A  normal  glide  over  trees  will  bring  a  machine 
a  long  way  across  the  field  before  it  touches 
the  ground  at  all.  The  result  will  be  similar 
in  either  case. 

For  the  same  reason,  fields  surrounded  by 
houses  or  other  buildings  should  be  avoided. 
Whenever  possible  then,  make  for  open 
country. 

Then  again,  the  shape  of  the  field  selected 


PRACTICAL  FLYING  39 

is  of  the  utmost  importance.  Some  fields 
are  long  and  narrow;  such  a  field  is  quite 
all  right  provided  the  wind  is  blowing  ap- 
proximately up  or  down  it.  It  is,  however, 
a  mistake  to  try  and  land  in  the  length  of  a 
long  field  if  a  strong  side  wind  is  blowing. 

It  is  always  essential  to  land  as  nearly  into 
the  wind  as  possible.  Try  then  and  select  a 
field  whose  lengthways  happens  to  be  against 
the  wind.  The  direction  of  the  wind  is  best 
indicated  by  smoke;  this  should  always  be 
looked  for. 

The  next  consideration  is  the  slope  of  the 
ground.  Gentle  slopes  are  not  easily  dis- 
cernible from  a  height,  but  they  should  be 
carefully  watched  for.  A  steepish  slope  should 
be  detected  without  much  difficulty.  River 
valleys  will  help  to  give  a  general  indication 
of  the  lie  of  the  land.  Flat  ground  should 
always  be  tried  for.  If  only  sloping  ground 
is  available,  select  a  patch  wThich  can  be 
approached  uphill  and  against  the  wind. 

In  the  same  way,  if  plough  is  the  only 
ground  within  reach,  select  a  place  where  the 
plough  is  cut  up  and  down  the  particular 


40  THE  FLYER'S  GUIDE 

direction  of  the  wind — that  is  to  say,  land 
along  the  plough  provided  it  is  also  against 
the  wind. 

On  all  occasions  select  a  place  where  mis- 
judgment  will  have  the  least  evil  consequences. 
For  example,  do  not  select  the  edge  of  a 
precipice  or  even  the  sides  of  a  railway  cut- 
ting. 

It  is  of  course  more  convenient  to  land  near 
a  road  if  help  is  required.  Such  a  considera- 
tion, however,  should  be  taken  into  account 
after  all  others.  Do  not  risk  a  smash  in 
order  to  get  near  a  road.  When  landing 
over  a  road  or  a  railway,  bear  in  mind  that 
there  are  almost  certain  to  be  telegraph  wires 
to  land  over.  Now,  telegraph  wires  are  in- 
visible from  above,  but  the  poles  are  not. 
Always  keep  a  sharp  lookout  for  the  latter 
when  making  a  descent  near  a  road  or  rail- 
way. 

A  few  general  hints  may  prove  of  value  to 
the  uninitiated. 

Firstly  always  take  a  little  money  when 
flying  across  country.  It  will  be  found  very 
useful  if  forced  to  descend  in  strange  parts. 


,0  be  taken  , 

lni£  Room 

PRACTICAL  FLYING  41 

A  smoke  and  a  match  may  prove  of  some 
comfort  to  the  smoker  who  has  to  survey  the 
remains  of  his  erstwhile  flying  machine! 

Even  nowadays  the  sight  of  an  aeroplane 
still  attracts  a  large  crowd  of  inquisitive 
yokels.  Try  and  prevent  them  from  breaking 
up  the  machine,  or  even  its  remains,  if  you 
do  have  to  land  hi  the  country.  If  possible 
a  local  policeman  should  be  put  in  charge  of 
it  while  you  go  and  telephone  for  help. 

If  the  machine  has  to  be  left  out  all  night, 
it  should  be  wheeled  to  the  most  sheltered 
corner  of  the  field,  placed  head  to  wind,  and 
pegged  down.  Screw  pickets  are  the  best 
things  to  use  as  pegs.  The  machine  should 
then  be  picketed  down  at  both  wheels  and 
at  each  wing  tip.  In  addition  the  tail  should 
be  secured  to  the  ground.  The  propeller, 
engine,  and  seating  accommodation  should 
be  covered  over  if  covers  can  possibly  be 
procured. 

The  above  paragraphs  only  refer  to  flying 
as  such,  and  contain  no  mention  of  the 
training  required  to  apply  same  to  the  ex- 
igencies of  modern  warfare.  Such  references 


42  THE  FLYER'S  GUIDE 

are  included  in  the  scope  of  many  other 
publications,  this  work  being  entirely  con- 
fined to  an  elementary  treatise  on  the  prac- 
tice of  aviation  alone. 


CHAPTER  III 

THE  CONSTRUCTION  OF  AEROPLANES.   THEIR 
CARE  AND  MAINTENANCE 

AN  aeroplane  is,  or  should  be,  constructed 
in  such  a  manner  as  to  get  a  maximum  of 
strength  with  a  minimum  of  weight.  Roughly 
speaking,  the  planes,  which  form  the  lifting 
surface  of  a  machine,  are  built  about  a  body 
or  fuselage  in  which  the  engine,  fuel,  and  pilot 
are  accommodated.  Underneath  a  landin 
carriage  has  to  be  provided.  A  stabilising 
plane  at  a  distance  from  the  main  planes  is 
also  essential.  In  modern  machines  this  is 
always  behind,  and  is  known  as  the  tail  plane. 

The  construction  of  a  main  plane  will, 
therefore,  be  now  briefly  described.  In  flight 
the  planes  are  subject  to  a  constant  reaction. 
It  is  this  reaction  which  provides  the  lift. 
In  horizontal  flight  this  reaction  must  be 
equal  to  the  total  weight  lifted.  Therefore 
the  total  weight  lifted  divided  by  the  area 

43 


44  THE  FLYER'S  GUIDE 

of  the  plane  surface  gives  the  normal  loading 
per  unit  area.  The  loading  per  square  foot 
of  course  varies  with  different  machines,  but 
6  Ibs.  per  square  foot  may  be  taken  as  a 
fair  average.  As  the  speed  of  the  aeroplane 
increases  (e.g.  in  a  steep  nose  dive),  the  re- 
action on  the  planes  also  increases,  the  re- 
action varying  as  the  square  of  the  velocity. 

With  this  consideration  before  you,  and 
also  the  fact  that  a  considerable  factor  of 
safety  has  to  be  provided,  you  will  appre- 
ciate that  a  plane  has  to  be  of  very  sound 
construction. 

The  design  of  a  plane  then  is  governed  by 
the  following  principles: 

(1)  The  attainment  of  requisite  strength; 

(2)  The  saving  of  every  ounce  of  weight; 

(3)  The  choice  of  such  a  section  as  will 

conduce  to  efficiency. 

All  planes  are  cambered  in  section,  the 
top  surface  being  of  a  very  pronounced  camber 
while  the  lower  surface  is  usually  almost  flat 
(in  some  machines  it  is  quite  flat).  About 
two-thirds  of  the  lift  is  derived  from  the 


THE  CONSTRUCTION  OF  AEROPLANES  45 

vacuum  created  above  the  top  surface.  A 
pronounced  camber  on  the  lower  surface  tends 
to  increase  the  head  resistance  while  not 
materially  affecting  the  lift. 

The  centre  of  pressure  on  a  plane  varies 
with  the  angle  of  incidence,  but  in  normal 
flight  on  an  average  it  may  be  assumed  to 
be  about  one-third  of  the  chord  from  the 
leading  edge.  As  the  speed  increases  the 
centre  of  pressure  moves  back,  possibly  hi 
practice  up  to  a  limit  of  about  two-thirds 
of  the  chord  from  the  leading  edge. 

In  practice  the  whole  work  thrown  on  the 
plane  is  borne  by  two  spars.  These  are 
usually  situated  approximately  as  hi  diagram 
B  below,  but  in  many  cases  the  front  spar 
is  coincident  with  the  leading  edge.  The 
external  bracing  of  the  spars  varies  in  dif- 
ferent types  of  machines,  which  will  be  dealt 
with  later;  but,  however  supported,  they  are 
subjected  to  a  bending  moment  which  is  a 
maximum  at  the  centre  point  between  two 
supports  and  vanishes  to  zero  when  actually 
at  the  point  of  support.  They  are  also  sub- 
jected to  a  shearing  force,  which  is  a  max- 


46  THE  FLYER'S  GUIDE 

imum  at  the  points  of  support  (always  as- 
suming the  structure  to  be  rigid)  and  vanishes 
to  zero  at  the  centre  point  between  two 
supports.  Assuming  the  structure  to  be  rigid, 
the  breaking  strain  of  a  spar  will  then  vary 
as  its  breadth  to  the  power  of  one  and  as 
the  square  of  its  depth.  The  necessary 
strength  consistent  with  lightness  can  there- 
fore be  best  obtained  by  making  the  spar 
deep  and  thin.  This  method  of  obtaining 
strength  is,  however,  strictly  limited  by  the 
shape  of  the  wing  curve,  which  it  is  desired 
to  employ.  In  order  to  obtain  the  best 
stream  lines  the  plane  section  should  be  fairly 
deep  in  front,  tapering  to  a  point  at  the 
trailing  edge.  This  enables  one  to  have  a 
fairly  deep  front  spar,  the  depth  of  the 
back  one,  however,  being  considerably  cur- 
tailed. To  make  up  for  the  loss  of  depth 
the  back  spar  has  to  be  of  considerable 
breadth.  In  flight  there  is  a  tendency  for 
the  planes  to  fold  backwards,  due  to  pressure 
of  the  air  stream  on  them. 

This  tendency  is  resisted  in  all  planes  by 
compression  stays  and  internal  bracing  wires. 


:s  Li 
'tel  m  Reading  Roc:  - 

THE  CONSTRUCTION  OF  AEROPLANES    47 

In  some  machines  there  are  also  external 
bracing  wires  to  prevent  the  wings  folding 
backwards.  These  are  known  as  drift  wires. 
Diagram  A  shows  the  internal  construction 
of  a  plane  in  plan.  This  is  not  a  scale  draw- 
ing and  does  not  represent  any  particular 
plane.  It  is  only  shown  as  an  example. 

The   leading   and   trailing   edges   are   not 
shown  in  the  diagram. 


DIAGRAM  A. 

A  B  is  the  front  spar.  C  D  is  the  rear 
spar.  L  M  and  N  P  are  compression  stays. 
B  M  and  L  P  are  internal  drift  wires.  N  M 
and  L  D  are  internal  anti-drift  wires. 

The  spars  are  fixed  to  the  fuselage  or  body 
of  the  machine  at  B  and  D.  A  and  C  are 
the  outside  ends  of  the  spars.  As  the  wind 
pressure  tends  to  force  the  plane  to  fold 
backwards,  the  wire  B  M  tightens  up  and 
prevents  the  rear  spar  from  folding  back- 


48  THE  FLYER'S  GUIDE 

wards.  The  tendency  is  also,  of  course,  to 
push  the  front  spar  back  so  that  the  com- 
pression stay  L  M  is  at  once  put  in  a  state 
of  compression,  thus  preventing  the  front 
spar  from  folding  back.  Exactly  similar  work 
is  done  by  the  wire  L  P  and  the  compression 
stay  P  N.  Thus  the  whole  wing  is  kept 
rigid  in  a  fore  and  aft  sense.  One  might 
have  three  or  four  or  more  compression  stays 
in  a  plane,  but  two  is,  I  think,  the  com- 
monest number.  As  I  have  already  pointed 
out,  reduction  of  unnecessary  weight  through- 
out the  machine  is  essential. 

When  in  flight,  the  drift  wires  B  M  and 
L  P  being  taut,  the  anti-drift  wires  L  D  and 
N  M  become  slack  and  do  no  work. 

If,  however,  the  machine  is  subject  to  a 
sudden  loss  of  forward  way  (i.e.  on  a  heavy 
land  or  taxying  over  rough  ground)  the  planes 
then  tend  to  go  on.  The  anti-drift  wires 
immediately  become  taut  and  keep  the  struc- 
ture rigid  in  the  same  manner  as  the  drift 
wires  do  in  flight. 

Spars  are  usually  made  of  either  ash  or 
silver  spruce.  Given  two  spars  of  the  same 


THE  CONSTRUCTION  OF  AEROPLANES  49 

section,  one  ash  and  the  other  silver  spruce, 
the  ash  would  give  the  higher  breaking  strain. 
Owing  to  the  fact  that  ash  is  heavier  than 
spruce,  this  advantage  is  more  or  less  counter- 
balanced, because  a  thicker  spruce  spar  can 
be  employed  for  the  same  weight.  Ash  for 
practical  purposes  has  another  disadvantage. 
It  has  to  be  thoroughly  seasoned  for  about  a 
year  before  use,  and  seasoned  ash  is  rare. 
The  majority  of  spars  on  present-day  ma- 
chines are  therefore  made  of  silver  spruce. 

Compression  stays  usually  consist  of  either 
hollow  box  ribs  or  steel  tube.  They  fit  into 
sockets,  generally  steel,  which  are  clipped 
round  the  spar.  Spars  should  not  be  drilled 
to  take  fittings,  as  they  will  thereby  be 
slightly  weakened.  The  drift  (and  anti-drift) 
wires  are  attached  to  steel  clips,  and  made 
adjustable  by  turn-buckles. 

In  most  planes  you  will  find  the  positions 
of  the  spars,  leading  and  trailing  edges,  ap- 
proximately as  in  diagram  B  (as  noted  above, 
the  front  spar  and  leading  edge  are  some- 
times coincident).  The  leading  edge  is  not 
meant  to  take  any  appreciable  load,  and 


50 


THE  FLYER'S  GUIDE 


consists  of  some  light  wood  rounded  off  in 
front.  The  trailing  edge  has  no  thickness, 
and  may  consist  of  a  piece  of  string,  stretched 
from  rib  to  rib,  to  support  the  fabric.  Ribs 
run  from  the  leading  to  the  trailing  edges 


L  t  ADI  HIS      tDGt 


/ 


7KAIUNG  CD6C 

DIAGRAM  B. — SHOWING  UNCOVERED  PLANE  IN  PLAN. 


Rib 


DIAGRAM  C. — SHOWING  APPROXIMATE  SECTION  OF  A  PLANE 

THROUGH  A  RlB. 

at  intervals  of  about  18  inches.     These  are 
only  to  support  the  fabric,  and  are  usually 
made  of  three-ply.     Holes  are  generally  bored 
in  the  ribs  to  lighten  them. 
A  rib  consists  of  a  web  with  a  flange  on 


THE  CONSTRUCTION  OF  AEROPLANES  51 

top  and  bottom  (width  of  flanges  about  1 
inch).  The  fabric  is  tacked  on  through  the 
centre  of  the  flanges,  so  that  the  tack  passes 
down  the  web  of  the  rib. 

In  flight  the  resultant  reaction  on  a  plane 
is  at  right  angles  to  it.  This  resultant  can 
be  resolved  into  two  forces  at  right  angles 
to  each  other,  the  one  horizontal,  the  other 
vertical.  The  former  is  called  drift,  the  latter 
lift.  Having  briefly  considered  the  construc- 
tion of  a  plane  in  so  far  as  the  withstanding 
of  drift  is  concerned,  it  would  now  appear 
appropriate  to  add  a  few  notes  on  lift  and 
anti-lift  bracings. 

There  are,  of  course,  many  variations  in 
bracings,  but  the  two  main  types  are: 

(1)  Monoplanes; 

(2)  Biplanes. 

(1)  The  ordinary  type  of  monoplane  con- 
sists of  a  fuselage,  in  the  front  of  which  the 
engine  is  mounted,  with  the  pilot  and  pas- 
senger behind  the  engine.  One  set  of  planes 
is  mounted  on  each  side  of  the  fuselage. 
The  spars  of  the  wings  are  either  pinned  to 


* 

52  THE  FLYER'S  GUIDE 

a  fitting  on  the  fuselage,  or  else  pass  through 
steel  guides  into  the  fuselage,  being  pinned 
together  (that  is  the  two  front  ones  together 
and  the  two  back  ones  together)  in  the  centre 
inside. 

Some  monoplanes,  of  the  parasol  type,  have 
the  planes  mounted  above  the  fuselage,  thus 
affording  the  pilot  a  clear  field  of  vision 
directly  below  him.  The  general  principles 
of  bracing  are,  however,  identical  with  those 
of  an  ordinary  monoplane. 

The  planes  are  kept  in  place  by  high  tensile 
steel  wire  or  cables  from  above  and  below 
the  fuselage.  (Cables  are  used  more  than 
wires  for  this  purpose.) 

Now,  in  flight  the  tendency  is  to  lift  the 
planes,  therefore  the  bracings  from  below  do 
all  the  work,  the  top  bracings  being  slack. 
The  former  are  called  flying  wires,  the  latter 
landing  wires.  When  on  the  ground  the 
planes,  being  subject  only  to  the  force  of 
gravity,  tend  to  drop.  Therefore  the  land- 
ing wires  do  all  the  work  on  the  ground, 
the  flying  wires  becoming  slack.  These  brac- 
ing wires  or  cables  are  attached  to  a  fitting 


THE  CONSTRUCTION  OF  AEROPLANES    53 

on  the  spar.  In  most  monoplanes  there  are 
three  wires  to  each  spar;  in  some  small-span 
machines,  however,  there  may  be  only  two. 
The  top  support  for  the  bracing  wires  is 
furnished  by  a  cabane,  usually  composed  of 
four  steel  tubes  (two  from  each  side  of  the 
fuselage)  which  meet  at  the  top.  In  a 
similar  manner  a  lower  cabane  is  provided 
below  the  fuselage  to  take  the  flying  wires. 
In  many  machines  a  cabane  is  only  provided 
to  take  the  rear  spar  flying  wires,  the  front 
ones  being  attached  to  some  part  of  the 
landing  chassis. 

(2)  A  tractor  biplane  consists  of  a  fuselage 
with  engine  and  propeller  in  front,  with  two 
sets  of  planes,  one  above  the  other.  The 
lower  planes  are  attached  to  the  sides  of 
the  fuselage  in  a  similar  manner  to  those  of 
a  monoplane,  but  lower  down.  The  method 
of  attaching  the  top  planes  varies,  but  one 
method  is  as  under. 

Two  struts  project  upward  from  each  side 
of  the  fuselage,  and  to  these  is  attached  a 
small  centre  top  plane  kept  in  position  by 
cross-bracing  wires.  The  total  length  of  this 


54 


THE  FLYER'S  GUIDE 


plane  will  then  be  equal  to  the  breadth  of 
the  fuselage.  The  outside  top  planes  are 
then  pinned  to  this  centre  section  and  kept 
in  position  by  bracing  as  under. 

L  M  is  top  left-hand  plane.  A  B  is  bottom 
left-hand  plane.  P  K  and  M  B  are  the  inter- 
plane  struts. 


DIAGRAM  D. — SHOWING  BRACING  OF  TRACTOR  BIPLANE  (FROM 
FRONT). 

There  are  of  course  two  similar  struts 
behind  P  K  and  M  B  (being  exactly  behind, 
they  do  not  appear  in  the  diagram).  These 
struts  fit  into  sockets  on  the  spars. 

A  P  and  K  M  are  the  flying  wires  (there 
are,  of  course,  two  similar  wires  behind  these 
bracing  the  rear  spars).  LK  and  PB  are 


••dni*  Roort 


THE  CONSTRUCTION  OF  AEROPLANES  55 

the  landing  wires,  there  being  two  similar 
ones  for  the  back  spars. 

In  flight  A  P  and  K  M  become  in  tension 
(the  landing  wires  being  slack),  thus  putting 
the  inter-plane  struts  in  compression.  The 
top  spars  are  thus  put  hi  a  state  of  com- 
pression and  bottom  spars  hi  one  of  tension. 
The  biter-plane  struts  are  kept  in  position 
fore  and  aft  by  incidence  wires  (ordinary 
cross  bracing).  The  whole  structure  then 
becomes  a  rigid  Warren  girder. 

S  K  is  shown  as  an  additional  flying  wire. 
This  should  not  be  necessary,  but  forms  a 
standby  if  one  of  the  other  flying  wires  break. 
If  S  is  on  the  front  of  the  landing  chassis, 
and  is  in  front  of  K,  S  K  also  becomes  an 
external  drift  wire.  On  the  ground  the  land- 
ing wires  L  K  and  P  B  do  all  the  work  of 
supporting  the  weight  of  the  planes. 

The  bracing  of  pusher  biplanes  is  identical 
to  the  above,  but  in  some  machines  of  the 
pusher  type  the  lower  plane  is  in  one  piece, 
with  the  nacelle  bolted  down  on  the  spars 
thereof. 

The  duplication  of  all  flying  wires  is  very 


56  THE  FLYER'S  GUIDE 

necessary,  especially  in  these  times  when  it 
is  no  uncommon  thing  to  have  them  cut  by 
bullets  during  an  aerial  fight. 

The  correct  rigging  and  tracing  up  of 
planes  is  greatly  facilitated  by  fitting  adjust- 
able turn-buckles  to  all  wires  and  cables. 

Now  practically  every  tractor  machine, 
monoplane  or  biplane  (there  may  be  a  few 
exceptions,  such  as  the  Caudron),  has  an 
enclosed,  or  partially  enclosed,  fuselage. 

A  fuselage  is  composed  four  longerons, 
usually  of  ash,  (two  on  each  side,  one  top 
and  one  bottom),  supported  at  frequent  inter- 
vals by  vertical  and  horizontal  struts  cross- 
braced  with  high-tensile  steel  wire.  It  is  sel- 
dom possible  to  get  pieces  of  ash  long  enough 
to  make  the  longeron  in  one  piece,  therefore 
two  pieces  spliced  together  have  to  be  used. 
No  strength  is  lost  in  a  good  splice. 

In  pusher  machines  tail  booms  are  made 
of  either  steel  tube  or  wood  (usually  silver 
spruce).  These  are  also  kept  in  a  rigid  po- 
sition by  means  of  struts  and  cross  bracing. 
Engine  bearers  for  stationary  engines  should 
be  either  of  ash  or  steel  tube. 


THE  CONSTRUCTION  OF  AEROPLANES    57 

Rotary  engines  are  supported  by  steel 
plates  through  which  the  crankshaft  passes. 
The  latter  is  prevented  from  turning  by  means 
of  a  key  and  kept  hi  position  by  locking  nuts. 
Two  such  plates  are  always  employed.  In 
pushers  the  two  plates  are  on  the  same  side 
of  the  engine  (hi  front  of  it).  The  engine 
is  then  said  to  be  overhung. 

In  many  rotary  engined  tractors  both  plates 
are  also  on  the  same  side  of  the  engine  (be- 
hind it),  the  engine  in  such  a  case  also  being 
overhung.  In  that  case  the  crankshaft  (a 
non-revolving  part)  transmits  the  whole  weight 
of  the  engine  to  the  engine  bearers. 

In  cases  of  other  tractors,  however,  a 
front  engine  bearer  is  employed  between  the 
cambox  and  the  propeller  (only  one  back 
plate  is  then  necessary).  In  such  cases  the 
nose  piece  (a  revolving  part)  transmits  part 
of  the  weight  of  the  engine  to  the  engine 
bearers,  the  nose  piece  revolving  round  a  ball- 
bearing mounted  in  the  front  bearer.  Align- 
ment in  such  cases  is  more  difficult  to  obtain. 
Any  inaccuracy  of  alignment  will  strain  the 
nose  piece  and  may  cause  a  fracture. 


58  THE  FLYER'S  GUIDE 

It  is,  of  course,  essential  that  the  utmost 
care  should  be  given  to  every  detail  of  aero- 
plane construction.  Many  small  defects,  such 
as  the  breaking  of  oil  and  petrol  pipes,  often 
lead  to  considerable  trouble.  Petrol  and  oil 
pipes  usually  break  at  or  just  below  a  nipple, 
where  they  are  attached  to  a  tank  (or  car- 
burettor, etc.). 

The  vibration  in  an  aeroplane  is  very  great, 
and,  unless  nipples,  etc.,  are  made  sufficiently 
strong,  such  breakages  are  to  be  expected. 
Vibration  is  more  evenly  distributed  by  fit- 
ting pipes  with  a  curl  Jo  just  below  the 
points  of  support. 

Flexible  pipes  are  unlikely  to  break,  but 
most  of  them  suffer  from  the  great  disad- 
vantage of  not  being  able  to  withstand  petrol. 
They  also  kink  very  readily. 

Tail  planes  vary,  but  most  machines  have 
a  fixed  stabilising  plane  and  a  hinged  ele- 
vator. The  latter  is  necessary  so  that  the 
pilot  can  change  his  flight-path.  Some  ma- 
chines have  a  single  movable  surface  for  a 
tail,  which  performs  the  function  of  both  a 
stabilising  plane  and  of  an  elevator.  Some 


THE  CONSTRUCTION  OF  AEROPLANES    59 

tail  planes  are  cambered  in  section,  others 
are  flat.  Their  shape  (hi  plan)  also  varies 
from  rectangular  to  semi-circular.  The  prin- 
ciples of  their  construction  are  similar  to 
those  of  a  main  plane,  having  usually  one 
spar  to  take  the  load  and  a  series  of  ribs  to 
which  the  fabric  is  attached. 

Tail  planes  are,  hi  the  case  of  machines 
with  fuselages,  either  attached  to  the  top 
of  the  fuselage  by  means  of  clips  or  else  they 
are  made  in  two  pieces  on  either  side  of  the 
fuselage,  the  latter  being  reinforced  at  the 
points  of  attachment  by  a  strong  compres- 
sion piece.  They  are  also  stayed  from  above 
or  below  (or  both)  by  steel  tubes. 

Undercarriages  also  vary  considerably. 
Some  are  wooden,  others  are  made  of  steel 
tubes.  Whatever  the  particular  form,  an  un- 
dercarriage must  be  designed  so  as  to  give 
the  necessary  propeller-clearance  and  to  form 
a  strong  support  on  which  to  mount  the  wheels. 
The  wheels  must  be  considerably  in  front  of 
the  centre  of  gravity,  so  as  to  obviate  any 
possibility  of  the  machine  turning  on  its 
nose.  In  order  to  distribute  the  shock  of 


60  THE  FLYER'S  GUIDE 

landing  and  of  taxying  over  rough  ground, 
the  wheels  are  not  attached  rigidly  to  the 
undercarriage,  but  are  attached  through  the 
media  of  shock  absorbers.  The  commonest 
form  of  shock  absorber  is  the  rubber  type, 
but  Oleo  gear  are  now  also  used  to  a  con- 
siderable extent,  especially  on  several  of  the 
larger  weight-carrying  machines.  The  ordi- 
nary type  of  rubber  shock  absorber  consists 
of  a  number  of  thick  elastic  bands  stretched 
tightly  over  the  top  of  a  skid.  In  such  a 
case  there  would  be  two  skids  (one  on  each 
side),  and  the  axle  would  pass  across  over 
the  skids  and  under  the  rubbers.  The  wheels 
would  be  fitted  outside  the  skids  so  as  to 
revolve  round  the  axle.  The  axle  would  be 
kept  in  its  place  fore7and  aft  by  means  of 
tie  rods.  There  are,  of  course,  many  modi- 
fications in  details  of  various  designs,  but  the 
above  illustrate  the  main  principle. 

To  come  on  to  the  covering  of  planes. 
The  fabric  most  commonly  used  is  a  flax 
fabric,  which  should  be  fine  and  closely  woven 
and  left  unbleached.  If  a  sufficiently  large 
piece  of  fabric  is  available,  it  may  be  laid 


THE  CONSTRUCTION  OF  AEROPLANES  61 

over  the  upper  surface,  folded  around  the 
leading  edge  and  along  the  lower  surface, 
being  sewn  along  the  trailing  edge.  It  should 
be  arranged  so  as  to  lay  fairly  tight  over  the 
plane  before  being  sewn.  It  should  then  be 
tacked  (only  copper  tacks  being  employed) 
about  every  foot  along  the  ribs  on  both  upper 
and  lower  surfaces.  A  narrow  tape  and 
washers  are  placed  along  the  ribs  over  the 
fabric  before  putting  the  tacks  in.  If  the 
fabric  is  not  sufficiently  wide  to  allow  of 
its  being  folded  over  the  plane,  two  pieces 
should  be  sewn  together,  the  join  being  made 
to  lay  along  the  leading  edge. 

When  the  fabric  is  finally  in  place,  it  will 
be  doped,  two  coats  of  dope  being  necessary. 
The  dope  has  the  effect  of  tautening  the 
fabric.  When  the  second  coat  of  dope  is 
dry,  the  plane  is  then  varnished.  Varnish 
keeps  the  plane  weather-proof  to  a  certain 
extent  and  also  makes  a  nice  smooth  surface. 
The  smoother  the  surface,  the  less  the  skin 
friction.  When  doping  or  varnishing,  it  is 
important  to  keep  out  all  dust  and  dirt,  and 
also  to  see  that  the  hairs  are  not  coming  out 


62  THE  FLYER'S  GUIDE 

of  the  brush,  as  these  would  adhere  to  the 
plane  and  make  the  surface  rough.  Although 
it  is  very  necessary  to  keep  the  surface 
smooth,  on  no  account  must  the  fabric  be 
touched  up  with  sand-paper,  as  this  will 
cause  weakness. 

Lateral  control  is  given  to  the  pilot  by 
one  of  two  means. 

The  first  method  is  by  means  of  hinged 
flaps  or  ailerons,  the  second  by  warping  the 
rear  spar. 

Ailerons  are  hinged  to  the  rear  spar,  the 
trailing  edge  being  cut  away.  They  are  op- 
erated by  the  control  lever  (or  wheel)  by 
means  of  cables,  passing  over  pulleys  and 
attached  to  a  king  post  on  the  ailerons.  In 
every  modern  machine  ailerons,  when  em- 
ployed, are  of  the  balanced  type — that  is  to 
say,  when  the  aileron  on  one  side  is  pulled 
down,  that  on  the  other  side  is  pulled  up  at 
the  same  time. 

In  the  case  of  warping  wings,  the  tips  of 
the  rear  spars  are  pulled  down  and  up.  The 
effect  is,  of  course,  the  same  as  with  ailerons 
— namely,  to  increase  or  decrease  the  inci- 


THE  CONSTRUCTION  OF  AEROPLANES  63 

dence  of  the  plane.  In  the  case  of  a  mono- 
plane, where  wing-warping  is  still  the  most 
usual  form  of  lateral  control,  the  lift  wires 
to  rear  spar  pass  over  pulleys  hi  the  lower 
cabane  and  are  operated  by  the  control  lever 
so  as  to  warp  the  spar.  The  anti-lift  or 
landing  wires  to  the  rear  spar  are  continuous 
— that  is  to  say,  they  pass  over  pulleys  on 
the  upper  cabane,  the  ends  being  attached 
to  corresponding  points  of  the  rear  spars  on 
each  side  of  the  fuselage. 

Fore  and  aft  control  is  given  by  a  hinged 
elevator  or  horizontal  rudder.  The  elevator 
is  fitted  with  king  posts,  two  on  the  upper 
and  two  on  the  lower  surface.  Cables  are 
attached  to  these  and  passed  through  guides 
to  the  cotrol  lever,  by  means  of  which  the 
pilot  operates  the  elevator. 

Directional  control  is  given  by  a  vertical 
rudder,  actuated  through  the  media  of  king 
posts  and  cables  by  a  rudder-bar  in  the 
pilot's  seat. 

All  control  wires  should  be  duplicated  in 
case  one  breaks  in  the  air. 

Some  biplanes  have  one  plane  vertically 


64  THE  FLYER'S  GUIDE 

above  the  other;  others  have  the  lower  plane 
slightly  in  rear  of  the  top  one.  In  the 
latter  case  the  planes  are  said  to  be  staggered. 
Staggered  planes  are  slightly  more  efficient 
(about  4  per  cent.)  than  those  arranged 
vertically  above  one  another;  also,  in  the 
case  of  tractor  biplanes,  the  occupant  of  the 
front  seat  is  enabled  to  get  a  larger  field  of 
view  vertically  downwards  by  staggering  the 
planes. 

The  erection  of  machines  forming  so  im- 
portant a  lesson  for  all  intending  aviators 
should  be  studied  ab  initio.  Firstly  with 
reference  to  the  planes;  the  spars,  which 
are  cut  to  size  by  machinery,  are  fitted  with 
compression  stays,  ribs,  internal  bracing  wires, 
and  such  other  fittings  as  are  incidental  to 
the  design.  These  are  all  put  into  their 
correct  position  from  the  drawings,  and  finally 
trued  up  by  the  adjustment  of  the  turn- 
buckles  on  the  drift  and  anti-drift  wires.  In 
the  case  of  wing-warping  machines  it  is  in- 
teresting to  note  that  ribs  should  not  be  a 
dead-tight  fit,  as  a  little  play  is  necessary 
when  the  spar  is  warped.  Before  covering 


THE  CONSTRUCTION  OF  AEROPLANES    65 

the  planes  care  must  be  taken  to  see  that 
the  turn-buckles  are  locked,  whilst  all  wires 
and  metal  fittings  must  be  painted  to  pre- 
vent rust.  Drift  wires  should  be  duplicated. 
The  erection  of  biplanes  may  be  consid- 
ered under  two  categories: 

(1)  Those  machines  whose  lower  and  top 

planes  are  each  in  one  piece  with  the 
nacelle  built  on  to  the  lower  plane. 

(2)  Those  machines  whose  lower  and  top 

planes  are  each  in  two  pieces  built 
on  to  a  fuselage  (or  nacelle). 

(1)  In  the  former  case  the  first  thing  to 
do  is  to  erect  the  planes  as  under. 

The  positions  of  the  inter-plane  strut- 
sockets  are  marked  on  the  upper  surface  of 
the  lower  plane,  exactly  corresponding  po- 
sitions being  given  for  those  of  the  lower 
surface  of  the  upper  plane  by  superimposing 
the  planes. 

These  sockets  are  then  very  carefully  bolted 
in  position  and  the  planes  erected  by  insert- 
ing the  inter-plane  struts  and  bracing  wires. 
Great  care  must  be  taken  to  see  that  the 


66  THE  FLYER'S  GUIDE 

struts  are  placed  in  their  correct  positions. 
In  some  machines  the  rear  sets  of  struts  are 
not  interchangeable,  slightly  increasing  in 
length  on  one  side  from  the  centre  in  order 
to  counter-balance  the  torque  of  the  propeller. 
Front  and  rear  struts  are  not  always  inter- 
changeable. It  is,  therefore,  of  the  utmost 
importance  to  see  that  struts  are  exactly  as 
per  drawings.  During  this  time  the  lower 
plane  should  be  supported  under  the  spars  by 
low  trestles  or  some  similar  device. 

Now,  considering  the  front  or  rear  sets  of 
struts  separately,  a  pair  of  inter-plane  struts 
and  the  sections  of  upper  and  lower  spar 
between  them  form  a  rectangle  (that  is,  of 
course,  provided  the  struts  are  of  equal 
length).  Now,  the  diagonals  of  a  rectangle 
are  equal.  Therefore,  provided  you  have 
fitted  the  strut-sockets  accurately  and  that 
the  struts  are  also  accurate,  that  section  of 
the  planes  will  be  true  when  the  diagonals 
(e.g.  the  landing  and  flying  wires)  are  equal. 

If  the  struts  are  not  meant  to  be  quite 
the  same  length,  the  length  of  the  diagonals 
(e.g.  the  landing  and  flying  wires)  for  that 


THE  CONSTRUCTION  OF  AEROPLANES    67 

particular  section  must  be  obtained  from  the 
drawings  and  adjusted  accordingly.  Simi- 
larly each  section  of  the  plane  can  be  trued 
up,  as  far  as  is  concerned  by  the  landing 
and  flying  wires.  This  process  of  trueing  up 
should  be  commenced  at  the  centre  section 
of  the  planes,  the  incidence  wires  being  ad- 
justed as  far  as  possible  to  measurement 
simultaneously  with  the  flying  and  landing 
wires  of  each  section.  It  will  be  necessary 
and  more  convenient  to  finally  check  the 
incidence  after  the  machine  is  wholly  erected. 
Having  erected  the  planes,  the  tail  booms 
are  next  put  together  in  a  similar  manner 
by  very  carefully  fitting  the  inter-tail  boom 
struts  and  adjusting  them  with  then-  bracing 
wires.  The  tail  booms,  having  been  correctly 
rigged,  are  then  fitted  to  the  main  planes.  The 
ends  of  the  tail  booms  either  fit  into  sockets 
or  are  pinned  to  clips  fitted  on  the  rear  spars 
of  the  planes.  When  finally  erected,  the  load 
is  taken  by  the  bracing  wires  and  not  by  these 
fittings.  The  planes  and  tail  booms,  thus 
erected,  are  then  lifted  on  trestles  sufficiently 
high  to  allow  of  the  undercarriage  being  fitted. 


68  THE  FLYER'S  GUIDE 

In  most  types  of  machines  the  undercar- 
riage struts  fit  into  sockets  on  the  underside 
of  the  lower  plane  spars  (or  of  the  fuselage 
in  the  case  of  fuselage  machines).  The  under-, 
carriage  must  be  carefully  erected  about  a 
centre  line.  Care  must  also  be  taken  to  see 
that  strut,  sockets  are  fitted  at  the  correct 
angle  to  take  the  struts. 

It  is  not,  of  course,  possible  to  give  a 
detailed  description  of  the  erection  of  every 
type  of  machine,  but  it  is  considered  that 
once  the  main  principles  are  appreciated  such 
knowledge  should  be  applicable  to  any  ordi- 
nary type  of  which  drawings  are  available. 

Finally,  the  nacelle,  tail  plane,  elevator, 
rudder,  ailerons,  etc.,  may  be  fitted. 

The  angle  of  incidence  of  the  planes  is 
finally  checked  by  getting  the  machine  level 
laterally  and  chocking  the  tail  up  in  the 
flying  position.  The  incidence  is  then  meas- 
ured by  means  of  a  straight  edge  and  spirit 
level.  Incidence  is  given  in  inches  (not  de- 
grees). Sometimes  the  chord  is  taken  as 
between  the  two  spars,  sometimes  as  be- 
tween the  leading  and  trailing  edges.  These 


THE  CONSTRUCTION  OF  AEROPLANES  69 

details  will  always  be  found  on  the  drawings. 
The  straight  edge  is  placed  on  the  under 
surface  of  the  plane,  one  end  being  held 
lightly  against  the  rear  spar  (or  trailing  edge, 
according  to  the  data).  The  straight  edge 
is  then  kept  horizontal  by  means  of  the 
spirit  level,  and  the  difference  of  height  be- 
tween the  front  and  leading  edge  of  the  chord 
in  question  is  then  measured  in  inches.  The 
incidence  must  be  checked  at  regular  inter- 
vals along  the  planes.  The  incidence  is  cor- 
rected by  means  of  the  incidence  wires. 

(2)  The  erection  of  machines  whose  planes 
are  attached  to  each  side  of  a  fuselage  (or 
nacelle). 

The  first  thing  to  do  in  this  case  will  be 
to  erect  the  fuselage.  One  side  is  erected  at 
a  time.  An  easy  way  to  get  the  sides  of  the 
fuselage  correct  is  to  make  a  scale  drawing 
on  the  floor.  In  most  modern  fuselages  the 
longerons  are  decidedly  curved.  They  can 
be  kept  in  their  correct  position  while  the 
struts  are  being  fitted  by  nailing  little  wooden 
blocks  in  the  floor,  the  places  for  these  blocks 
being  shown  from  the  drawing  on  the  floor. 


70  THE  FLYER'S  GUIDE 

All  the  fittings  for  the  fuselage  struts  and 
wire  clips  must  be  put  on  the  longerons  pre- 
vious to  this.  The  longerons  being  tempo- 
rarily held  in  their  proper  places  as  described 
above,  the  struts  are  then  fitted  and  the 
whole  side  of  the  fuselage  is  made  to  as- 
sume its  permanent  shape  by  fitting  and 
adjusting  the  cross-bracing  wires. 

Having  got  the  two  sides  of  the  fuselage 
correct,  the  horizontal  struts  and  bracing 
wires  are  then  fitted  and  the  fuselage  is  then 
erected.  The  centre  section  of  the  top  plane 
is  then  fitted  to  the  fuselage  by  fitting  the 
four  inter-plane  struts  (two  on  each  side  of 
the  fuselage)  and  their  cross-bracing  wires. 
The  planes  are  then  erected  on  each  side  of 
this  structure  in  a  similar  manner  to  that 
described  above.  The  erection  of  the  re- 
mainder of  the  machine  is  also  in  principle 
as  described  above. 

The  procedure  of  erecting  a  monoplane  is 
similar  to  that  of  a  biplane  with  fuselage. 
Before  fitting  the  planes  the  cabanes  must  be 
fitted. 

In  all  cases  the  dihedral  angle  between  the 


THE  CONSTRUCTION  OF  AEROPLANES  71 

planes  (if  any;  where  the  upper  and  lower 
planes  are  each  only  in  one  piece  there  can 
of  course  be  no  dihedral)  is  correctly  adjusted 
by  means  of  the  landing  wires. 

Aeroplanes,  being  very  fragile,  require  con- 
stant attention  to  keep  them  in  an  efficient 
state. 

All  wires  must  at  all  times  be  covered  with 
a  thin  film  of  grease  to  keep  out  rust.  High 
tensile  steel  wire  or  steel  cable,  when  sub- 
jected only  to  a  direct  pull,  lasts  for  a  very 
long  time  providing  rust  is  kept  out.  Cables 
that  pass  over  pulleys  or  through  guides, 
however,  have  only  a  very  short  life  and 
must  be  constantly  inspected.  As  soon  as 
one  strand  is  seen  to  have  frayed  the  whole 
cable  should  be  replaced  by  a  new  one.  When 
one  strand  has  worn,  it  is  almost  invariably 
the  case  that  others  have  done  the  same,  al- 
though not  visible.  The  life  of  cables  run- 
ning over  pulleys  can  be  prolonged  by  ensur- 
ing that  they  pass  over  the  pulleys  at  the 
correct  angle  (i.e.  do  not  rub  against  the 
flanges).  The  rigger  on  a  machine  should 
carefully  inspect  all  wires  and  controls  every 


72  THE  FLYER'S  GUIDE 

night.  In  addition,  a  machine  should  be 
thoroughly  inspected  by  the  officer  in  charge 
of  it  at  least  once  a  week.  In  the  case  of 
machines  with  enclosed  fuselages,  the  latter 
should  be  uncovered  for  the  weekly  inspection. 
The  greatest  care  must  at  all  times  be  taken 
to  ensure  that  all  turn-buckles  have  locking 
wires.  Another  point  with  regard  to  turn- 
buckles  is  to  see  that  the  bolts  fitting  into 
them  are  sufficiently  engaged. 

It  is  of  the  utmost  importance  to  ensure 
that  aeroplanes  and  their  sheds  are  kept 
thoroughly  clean.  The  floors  of  most  sheds 
have  a  strip  of  sheet  metal  inset  up  their 
centre.  Care  must  be  taken  to  leave  ma- 
chines with  their  engines  over  this  metal 
part,  so  that  any  oil  that  drips  down  will 
drip  on  to  the  metal  and  not  on  to  the  wood 
flooring.  If  metal  is  not  provided  up  the 
floor  of  the  shed,  small  trays  must  be  placed 
under  the  engines  at  night. 

The  floor  of  a  shed  will  soon  become  cov- 
ered with  oil  unless  these  precautions  are 
taken,  with  the  result  that  tyres  will  suffer 
and  dust  and  dirt  accumulate. 


THE  CONSTRUCTION  OF  AEROPLANES  73 

Grease  and  oil  should  be  wiped  off  the 
planes  as  soon  as  a  machine  comes  in.  A 
dry  rag  will  be  employed  for  this  purpose. 
On  no  account  is  petrol  to  be  used,  as  it 
deteriorates  the  fabric. 

See  that  tyres  are  kept  sufficiently  tight. 
Shock  absorbers  must  also  be  carefully 
watched,  as  their  life  is  not  very  long,  especi- 
ally when  a  machine  is  constantly  landing 
on  or  taxying  over  rough  ground. 

Special  care  must  be  taken  hi  handling 
machines  of  the  pusher  type  with  tubular 
steel  outriggers.  If  these  outriggers  are  con- 
stantly being  lifted  they  are  very  liable  to 
lose  shape.  It  is  generally  possible  in  such 
cases  to  make  a  little  two-wheeled  truck  to 
fit  under  the  rudder  post.  This  saves  lifting 
the  tail  booms  when  man-handling  a  machine. 

When  filling  up  with  petrol  or  oil  it  is 
essential  to  use  a  filter. 


School  of  Military  Aeronautics  L'b---- 
Not  to  be  taken  from  Reading  Room 


CHAPTER  IV 

THE   THEORY   OF   FLIGHT 

CONSIDERING  the  question  from  the  most 
elementary  point  of  view  it  is  evident  that 
flight  is  only  a  dynamical  possibility;  or  in 
plain  words  a  flying  machine  is  only  sustained 
in  the  air  by  the  force  of  air  moving  past  it. 


B 


Now  the  air  flowing  past  an  aerofoil  causes 
a  reaction,  whose  resultant  acts  at  right  angles 
to  it.  Thus  if  A  B  is  an  aerofoil  meeting  a 
stream  of  air,  the  resultant  reaction  R  is 
at  right  angles  to  A  B. 

74 


THE  THEORY  OF  FLIGHT  75 

The  value  of  the  reaction  R  is  given  as 
being  equal  to  KSV2t.  It  is  not  intended  to 
give  a  quantity  of  formulae  or  equations,  but 
the  following  fundamental  equation  should  be 
carefully  noted,  as  much  may  be  learnt  from 
its  application: 

R  =  KSV'i. 

Where  R  =  total  reaction  in  kilogrammes. 

K  =  a  co-efficient  (which  varies  with  various 
wing  curves,  etc.). 

S  =  Surface'of  the  aerofoil  in  square  metres. 

V  =  Velocity  (in  metres  per  second)  of  the 
air  stream. 

i  =  Angle  at  which  the  aerofoil  meets  the 
stream  of  air,  measured  in  radians. 

Now,  a  force  can  be  resolved  into  any  two 
components  at  right  angles  to  each  other. 
Considering  our  aerofoil  as  the  planes  of  a 
practical  flying  machine,  the  resultant  reac- 
tion can  be  resolved  into  two  components, 
one  vertical,  the  other  horizontal. 

Furthermore,  it  is  obvious  that,  if  the 
machine  is  going  to  lift,  the  vertical  com- 
ponent of  the  reaction  must  be  equal  to  or 


76  THE  FLYER'S  GUIDE 

just  greater  than  the  total  weight  of  the 
machine. 

It  was  seen  from  the  fundamental  equation 
that  the  reaction  varies  as  the  surface,  the 
square  of  the  velocity,  and  the  angle  at 
which  the  planes  meet  the  air,  or,  as  it  is 
called,  the  angle  of  incidence,  and  a  co- 
efficient K,  which  is  a  constant  for  any  one 
form  of  plane. 

The  vertical  component  of  the  reaction  is, 
as  a  matter  of  fact,  equal  to  the  total  reac- 
tion x  cosine  of  the  angle  of  incidence,  and, 
where  the  latter  is  small,  as  it  must  be  in 
practice,  the  vertical  component  may  be  taken 
as  being  equivalent  to  the  total  reaction, 
cosine  0°  being  unity. 

Therefore  for  a  machine  to  lift  at  all,  the 
reaction  on  the  planes  must  be  a  certain 
value,  which  can  be  expressed  in  terms  of 
velocity,  surface,  and  angle  of  incidence. 

Thus  to  actually  make  any  machine  leave 
the  ground  (quite  apart  from  all  other  qual- 
ities which  are  essential  to  the  flying  machine) 
it  is  necessary  to  have  a  certain  plane  area 
passing  through  the  air  at  a  given  speed. 


THE  THEORY  OF  FLIGHT  77 

The  question  of  the  speed  required  to  bring 
about  a  condition  of  flight  and  of  the  power 
necessary  to  produce  that  speed  may  now 
be  considered  hi  conjunction  with  the  funda- 
mental formula. 

As  already  mentioned,  at  the  small  angles 
of  incidence  at  which  the  planes  of  a  flying 
machine  meet  the  ah*  hi  practice,  the  vertical 
component  is  almost  equal  to  the  total  reac- 
tion. The  smaller  the  angle  gets,  the  more 
nearly  are  they  equal,  until,  the  planes  being 
horizontal,  they  would  become  coincident,  and 
equal  to  zero! 

The  greater  the  vertical  component  the 
less  does  the  horizontal  component  become. 
(This  is  apparent  from  an  ordinary  parallelo- 
gram of  forces.)  The  horizontal  component 
of  the  reaction  represents  the  resistance  that 
the  planes  offer  to  being  drawn  through  the 
ah*. 

Besides  the  resistance  of  the  planes,  the 
resistance  created  by  the  other  parts  of  the 
machine,  such  as  struts,  wires,  fuselage, 
landing  chassis,  etc.,  must  now  be  considered. 
The  resistance  of  or  reaction  on  these  parts 


78  THE  FLYER'S  GUIDE 

varies  as  the  square  of  the  velocity  at  which 
they  are  travelling.  Consequently,  as  the 
speed  gets  higher  their  resistance  increases 
very  rapidly.  But  at  high  speeds  the  angle 
of  incidence  must  necessarily  be  small.  We 
can  see  this  from  the  fundamental  equation 
R  =  KSV%  because  V  varies  inversely  as  the 
square  root  of  i  for  any  given  machine. 

Now,  considering  the  resistance  of  the 
planes  only  (that  is,  leaving  out  of  account 
the  wires,  struts,  etc.),  up  to  a  limit  their 
resistance  decreases  at  higher  speeds  for  any 
given  machine,  because  they  are  at  a  smaller 
angle  of  incidence  and  therefore  meet  the 
wind  at  a  more  convenient  angle. 

The  total  resistance  of  the  machine,  that 
is,  the  resistance  of  the  planes  plus  the  re- 
sistance of  the  other  parts  of  the  machine, 
together  form  a  resistance  which  is  equal 
and  opposite  to  the  thrust  created  by  the 
propeller. 

Thus,  it  is  obvious  that  to  make  an  effi- 
cient aeroplane  this  total  resistance  must  be 
as  low  as  possible.  Without  going  into  for- 
mulae, it  can  be  assumed  that  the  total  re- 


THE  THEORY  OF  FLIGHT  79 

sistance  will  be  a  minimum  when  the  two 
resistances  are  equal.  The  angle  of  incidence 
at  which  this  occurs  is  easily  found. 

Now  to  come  on  to  the  question  of  power 
required  to  sustain  a  machine  in  horizontal 
flight. 

Power  is  merely  the  measure  of  the  rate 
of  doing  work.  If  one  is  employing  metric 
units,  it  is  measured  in  kilogramme-metre- 
seconds.  That  is,  the  work  done  in  one 
second  is  the  thrust  multiplied  by  the  dis- 
tance travelled  hi  that  time.  But  the  dis- 
tance travelled  through  hi  one  second  is  the 
velocity.  The  power  then  required,  to  sus- 
tain a  machine  in  horizontal  flight,  is  equal 
to  the  thrust  velocity.  But  thrust  varies 
as  the  square  of  the  velocity.  Therefore 
power  varies  as  the  velocity  cubed.  Conse- 
quently very  high-speed  machines  require 
enormous  power  (the  power  necessary  in- 
creasing very  rapidly  at  high  speeds). 

A  few  typical  curves  for  any  one  machine 
should  prove  the  best  method  of  amplifying 
the  ground  already  covered. 

As  has  already  been  seen  from  the  funda- 


80 


THE  FLYER'S  GUIDE 


mental  formulae  that  for  any  given  machine 

Va— 7=,   a   curve   can  therefore  be   plotted 
Vi 

showing,  for  any  one  machine,  how  speed 
required  for  flight  varies  with  the  angle  of 
incidence.  Without  professing  to  have  worked 
out  a  curve  for  any  particular  machine,  the 


Speeds 


\ 


Angles  of  /nc/aence 

DIAGRAM  E. 

curve  would  always  be  somewhat  after  the 
style  of  diagram  E. 

It  might  be  added  that  the  practical  limits 
for  the  angle  of  incidence  of  the  planes  of  a 
flying  machine  are  between  about  2°  and 
12°;  or  employing  circular  units,  which  are 
the  only  true  mathematical  measure  of  an 
angle,  as  between  .05  and  .20  radians. 


THE  THEORY  OF  FLIGHT 


81 


In  a  similar  manner  a  curve  can  be  plotted 
showing  how  the  thrust  for  any  one  ma- 
chine varies  according  to  the  angle  of  incidence. 

Again  without  professing  to  any  great  accu- 
racy, the  curve  will  be  something  after  the 
form  shown  in  diagram  F.  The  same  two 
practical  limits  for  the  angle  of  incidence  are 


Thrusts 


•20 


Angles  of  /nc/'dence. 

DIAGRAM  F. 

again  shown,  and  it  is  apparent  from  the 
curve  that  the  minimum  thrust  occurs  be- 
tween these  two  limits.  After  these  two 
limits  have  been  passed,  the  thrust  decreases 
very  rapidly,  especially  on  the  side  where  the 
angle  of  incidence  decreases. 

As  already  explained,  power  is  only  a  meas- 
ure of  the  rate  of  doing  work. 


82 


THE  FLYER'S  GUIDE 


Considering  the  case  of  an  aeroplane,  the 
power  required  to  sustain  it  in  horizontal 
flight  in  kilogrammetres  per  second  is  the 
thrust  x  distance  moved  through  in  one  sec- 
ond— that  is,  the  thrust  X  velocity. 


Any/es  of/stc/dence. 

DIAGRAM  G. 


Diagram  G  shows  the  speed  angle  of  inci- 
dence curve  and  the  thrust  angle  of  inci- 
dence curve  for  any  one  machine  plotted 
on  the  same  base  (speeds  and  thrusts  being 


THE  THEORY  OF  FLIGHT  83 

plotted  vertically,  and  angle  of  incidence 
horizontally). 

A  B  is  the  speed  angle  of  incidence  curve. 
C  D  is  the  thrust  angle  of  incidence  curve. 

Now  if  the  two  ordinates  are  multiplied 
together — that  is,  the  speeds  and  the  thrusts 
— a  curve  is  obtained  showing  useful  power 
required  for  any  angle  of  incidence  for  this 
given  machine. 

E  F  represents  the  approximate  shape  of 
this  curve  (diagram  G). 

From  this  curve  the  angle  of  incidence  can 
be  found  at  which  the  power  required  is  a 
minimum.  It  is  not  the  same  as  the  angle 
at  which  the  thrust  is  a  minimum,  but  is 
always  slightly  larger. 

This  should  be  fairly  apparent  now  that 
the  three  curves  are  together  on  one  base. 

It  is  a  very  easy  matter  to  convert  the 
power  angle  of  incidence  curve  into  a  power 
speed  curve,  since  a  speed  angle  of  incidence 
curve  has  already  been  obtained. 

It  is  apparent  from  this  latter  curve  that, 
as  the  angle  of  incidence  decreases,  the 
speed  increases;  consequently  the  power  speed 


84 


THE  FLYER'S  GUIDE 


curve  is  virtually  the  same  as  the  power 
angle  of  incidence  curve  the  other  way  round, 
but  slightly  elongated.  This  power  speed 


i 

/e 


Powers 


ang/e 
of 


Speed 
Com  spo/tding  to 


of  incidence 
20. 


Corrt 

ary/e 

of 


Speed 
spending  to 
of  incidence 

05. 


Speeds 

DIAGRAM  H. 


It  is 


curve  is  represented  in   diagram  H. 
known  as  the  "  aeroplane  curve." 

Now,  in  a  practical  flying  machine  the 
power  required,  as  found  from  that  curve, 
means  that  so  much  power  should  actually 
be  given  out  by  the  propeller. 


THE  THEORY  OF  FLIGHT  85 

Imagine  a  machine  fitted  with  an  engine 
of  nominal  80  horse-power;  that  does  not 
mean  that  the  power  given  out  by  the  pro- 
peller is  80  H.P.  The  inefficiency  of  the 
propeller  and  the  drive  have  to  be  considered. 
The  most  efficient  propeller  is  only  about 
75  per  cent,  efficient. 

Consequently  it  is  almost  impossible  to 
know  what  power  is  actually  given  out  by  a 
propeller  of  a  plant  of  some  nominal  horse- 
power. To  overcome  this  difficulty  makers 
supply  a  curve  with  their  plants  showing 
the  power  actually  given  out  by  the  propeller 
at  various  speeds. 

The  useful  power  given  out  by  a  propeller 
at  various  air  speeds  is  characteristically  of 
the  form  0  P  (diagram  K). 

This  is  known  as  the  propeller  curve.  The 
aeroplane  curve  F  E  (originally  found  in 
diagrams  G  and  H)  is  also  plotted  on  the 
same  speed  base  as  the  aeroplane  curve  in 
diagram  K. 

Now,  if  the  propeller  curve  cuts  the  aero- 
plane curve  hi  two  places,  as  it  does  in  the 
diagram,  then  the  aeroplane  would  fly  at 


86 


THE  FLYER'S  GUIDE 


the  two  speeds  corresponding  to  the  points 
of  intersection  of  the  curves  with  the  engine 
full  on. 

At  any  intermediate  speed,  unless  the  en- 
gine is   throttled   down,   the   aeroplane  will 

A 


Powers 


Corre 

>' 
of 


Speed 
sponding  to 
of  incidence 
2O. 


Corrt 

eno/e 

of 


Speed 
spondvy  to 
of  incidence 

05. 


Speeds. 

DIAGRAM  K. 


tend  to  rise.  In  practice  a  machine  is  usually 
designed  to  fly  at  the  highest  of  these  two 
speeds.  However,  horizontal  flight  can  be 
maintained  at  any  speed  between  these  two 


THE  THEORY  OF  FLIGHT  87 

points  by  manipulation  of  the  throttle  and 
elevator. 

Horizontal  flight  cannot  be  maintained  at 
any  speed  outside  these  points  owing  to  the 
power  being  insufficient.  These  curves  there- 
fore show  the  range  of  speed  of  a  machine. 

The  greatest  distance  between  the  curves 
XY  shows  the  maximum  excess  of  power, 
and  the  speed  corresponding  to  that  excess 
of  power  is  the  speed  at  which  the  aeroplane 
will  climb  fastest. 

If  the  curves  only  just  touch,  that  means 
that  the  propeller  is  only  just  giving  out 
sufficient  power  to  sustain  the  machine  in 
horizontal  flight,  and  therefore  it  will  not 
climb.  If  the  curves  do  not  touch  at  all, 
it  means  that  insufficient  power  is  being 
given  out  by  the  propeller  to  even  maintain 
horizontal  flight. 

Having  disposed  of  a  few  of  the  elements 
of  dynamic  flight  the  study  should  now  be 
completed  by  a  brief  reference  to  the  ques- 
tion of  stability. 

It  is  common  knowledge  that  the  planes 
of  any  practical  flying  machine  are  cam- 


88  THE  FLYER'S  GUIDE 

bered  in  section.  In  some  cases  the  lower 
surface  is  flat,  or  almost  flat,  but  the  upper 
surface  is  always  cambered. 

Now  a  cambered  plane  meeting  a  stream 
of  air  at  any  angle  of  incidence  less  than 
about  15°  is  inherently  unstable.  And  as 
we  have  already  seen  that  for  a  practical 
machine  the  incidence  must  be  less  than 
that,  therefore  in  practice  a  cambered  plane 
is  unstable.  At  the  present  moment  fore 
and  aft  stability  only  is  under  consideration. 
To  take  an  example.  Imagine  a  machine 
(with  cambered  planes)  flying  horizontally 
so  that  the  centre  of  pressure  is  coincident 
with  the  centre  of  gravity  and  that  the  ma- 
chine is  in  equilibrium.  Suppose  now  that 
this  state  of  equilibrium  is  disturbed  and 
that  the  tail  drops  slightly — that  is  to  say, 
the  angle  of  incidence  is  slightly  increased; 
then  the  centre  of  pressure  moves,  but  it 
moves  forward  and  becomes  in  front  of  the 
CG.  The  result  is  that  a  couple  is  set  up 
between  the  weight  acting  through  the  CG 
and  the  reaction  acting  through  the  CP, 
which  causes  the  tail  to  drop  still  more. 


THE  THEORY  OF  FLIGHT  89 

Therefore,  if  a  machine  consisted  of  a 
single  cambered  surface  only,  it  would  be 
inherently  unstable  fore  and  aft. 

A  flat  plane  on  the  other  hand  would  be 
stable  in  so  far  as  the  movement  of  the  CP 


DIAGRAM  I*-^— FIGURE  SHOWING  MOVEMENTS  OF  CP  WITH 
VARIOUS^  ANGLES  OF  INCIDENCE  FOR  TYPICAL  CAMBERED 
PLANE.:"' 

'V  ****"  S"  • 

~r*4      "* 

was  con^ern&L  With  a  flat  plane  at  0°, 
of  course,  there  would  be  no  vertical  reaction. 
At  just  more  than  zero  the  CP  would  be 
well  forward  and  would  move  back  until  at 
right  angles  to  the  air  stream  it  would  be 
half  way. 


90 


THE  FLYER'S  GUIDE 


However,  flat  planes  cannot  be  used  as  the 
lifting  surface  on  a  flying  machine  owing  to 
their  inefficiency.  Therefore,  a  cambered 


DIAGRAM    M. — FIGURE    SHOWING    MOVEMENT    OF    CP    WITH 
VARIOUS  ANGLES  OF  INCIDENCE  FOR  FLAT  PLANE. 


plane  must  be  used  and  some  device  employed 
to  overcome  this  inherent  instability. 

Consider  an  aeroplane  in  horizontal  flight. 
There  are  four  forces  acting  on  it,  and  they 
must  be  in  equilibrium. 

These  forces  are: 

(1)  The  weight  of  the  machine  acting 

vertically  downwards; 

(2)  The  lift  acting  vertically  upwards; 


THE  THEORY  OF  FLIGHT 


91 


(3)  The  thrust  created  by  the  propeller 

acting  along  the  line  of  flight; 

(4)  The    total    head    resistance  of    the 

whole  machine  acting  against  the 
line  of  flight. 

The  designer's  object  is  to  get  all  these 
four  forces  to  pass  through  the  centre  of 
gravity  when  the  machine  is  in  normal  hori- 


zontal flight.  The  machine  will  then  obvi- 
ously be  in  equilibrium,  as  there  will  be  no 
disturbing  element.  If  these  forces  do  not 
quite  coincide  through  the  centre  of  gravity, 
then  the  couple  of  the  thrust  and  head  re- 
sistance must  be  made  to  balance  the  couple 
of  the  lift  and  the  weight.  In  any  case  these 


92 


THE  FLYER'S  GUIDE 


four  forces  must  be  nearly  coincident  through 
the  centre  of  gravity. 

Diagram  N  represents  a  machine  under 
the  influence  of  these  four  forces. 

G  is  the  centre  of  gravity.  In  this  case 
the  couple  of  the  thrust  and  head  resistance 
tend  to  turn  the  nose  of  the  machine  down- 


wards, whereas  the  couple  of  the  reaction 
and  the  weight  tend  to  keep  it  up.  There- 
fore, these  couples  could  be  made  to  counter- 
balance each  other. 

Diagram  P  represents  another  case  where 
the  line  of  head  resistance  is  above  the  CG 
and  the  thrust  below  it,  the  reaction  again 
acting  in  front  of  the  CG.  In  this  case,  then, 
both  couples  tend  to  turn  the  nose  upwards, 


THE  THEORY  OF  FLIGHT  93 

and  the  machine  could  never  be  in  equilib- 
rium. 
There  are  three  kinds  of  equilibrium. 

(1)  Stable  equilibrium. 

A  body  in  a  state  of  stable  equilibrium  is 
in  such  a  state  that  if  disturbed  by  an  out- 
side force  it  will  come  back  to  its  original 
state. 

(2)  Neutral  equilibrium. 

A  body  in  a  state  of  neutral  equilibrium 
when,  if  disturbed,  it  will  remain  in  that 
disturbed  position. 

(3)  Unstable  equilibrium. 

A  body  is  in  unstable  equilibrium  when,  if 
disturbed,  it  tends  to  go  still  further  from 
its  original  state. 

Therefore,  it  is  desirable  to  keep  an  aero- 
plane in  a  state  of  stable  equilibrium. 

We  have  seen  from  the  foregoing  that  an 
aeroplane  having  only  one  cambered  surface 
cannot  be  stable.  To  make  it  stable  we 
have  to  employ  another  surface  at  a  dis- 
tance from  it.  Part  or  the  whole  of  this 


94  THE  FLYER'S  GUIDE 

surface  must  be  movable  and  in  practice  we 
know  it  nowadays  as  the  tail  plane  and 
elevator. 

Furthermore,  it  is  essential  that  this  tail 
plane  should  form  a  \/  or  dihedral  angle 
with  the  main  planes. 

A  few  words  about  tail  planes.  The  tail 
plane  must  be  considered  as  part  of  the  whole 
aeroplane,  and  not  as  a  separate  entity. 

Tail  planes  may  be  designed  so  as  to  carry 
a  certain  portion  of  the  weight  of  the  aero- 
plane. They  may  be  designed  so  as  to  exert 
no  pressure  either  way,  and  in  some  cases 
they  are  designed  to  exert  a  negative  pres- 
sure in  normal  flight. 

In  practice  it  would  appear  that  the  middle 
course  is  found  the  most  satisfactory,  be- 
cause then  the  tail  plane  has  exactly  the 
same  effect  whether  the  motor  is  running  or 
not.  In  either  of  the  other  two  cases  the 
pressure  on  the  tail  plane  is  affected  by  the 
subtraction  of  the  slip  stream  when  the  motor 
is  shut  off. 

The  functions  of  the  tail  plane  as  a  stabiliser 
may  be  described  as  follows: 


THE  THEORY  OF  FLIGHT  95 

Suppose  a  disturbing  influence  tends  to 
make  the  tail  of  the  machine  drop.  As  it 
drops,  the  angle  of  incidence  on  the  tail  plane 
increases;  consequently  the  reaction  on  the 
tail  plane  increases  and  tends  to  lift  the  tail 
back  to  its  normal  position  again. 

On  the  other  hand,  if  the  nose  of  the 
machine  drops,  the  tail  plane  gradually  as- 
sumes a  negative  angle  of  incidence,  and 
consequently  top  pressure  tends  to  lower  the 
tail  into  its  normal  position  again. 

Another  point  with  regard  to  minimising 
the  effect  of  disturbing  influences  is  to  keep 
the  main  weights  concentrated,  as  far  as 
practicable,  around  the  centre  of  gravity. 

So  much  for  fore  and  aft  stability. 

The  question  of  stability  from  a  directional 
point  of  view  is  the  next  consideration. 

An  aeroplane  is  steered  by  means  of  a 
vertical  rudder. 

A  practical  aeroplane  consists  of  a  quan- 
tity of  material,  such  as  struts,  wires,  and  in 
many  cases  an  enclosed  fuselage,  which  form 
a  side  area,  or,  as  we  may  call  it  for  con- 
venience, fin  area. 


96  THE  FLYER'S   GUIDE 

It  is  obvious  that  it  is  not  possible  to  make 
a  machine  without  a  certain  amount  of  fin 
area,  but  this  fin  area  is  of  the  utmost  im- 
portance from  the  point  of  view  of  directional 
and  lateral  stability. 

It  would  be  found  impossible  to  steer  a 
machine  with  a  rudder  and  no  fixed  fin  area. 
Imagine  such  a  machine  (which  is  only  a 
theoretical  possibility)  in  the  act  of  turning. 
As  soon  as  the  rudder  is  put  over  it  presents 
a  certain  surface  to  the  wind,  thus  causing 
the  whole  machine  to  turn  about  its  centre 
of  gravity,  until  the  rudder  again  comes  into 
the  eye  of  the  wind,  but  the  machine  will 
continue  in  the  same  flight  path,  flying  par- 
tially sideways. 

Therefore,  to  steer  a  machine  it  is  essential 
to  have  a  fixed  side  surface  in  addition  to 
the  rudder. 

The  above  statement  is  only  strictly  true 
as  far  as  gliding  flight  is  concerned.  If  the 
engine  were  running  it  would  turn  owing  to 
the  effect  of  the  thrust. 

Now  consider  a  machine  turning  which  has 
a  fixed  side  surface  and  a  rudder.  As  soon 


THE  THEORY  OF  FLIGHT  97 

as  the  rudder  is  put  over  it  presents  a  surface 
to  the  air  stream  and  a  moment  is  created 
about  the  centre  of  gravity.  Therefore,  the 
machine  tends  to  turn  about  its  centre  of 
gravity.  Directly  the  machine  starts  to  turn, 
the  fixed  surface  presents  a  surface  to  the 
air  stream.  The  pressure  on  this  also  cre- 
ates a  moment  about  the  centre  of  gravity. 
As  soon  as  these  two  moments  about  the 
centre  of  gravity  are  equal  the  machine  ceases 
to  turn  about  its  CG. 

When,  however,  the  moment  of  these  two 
forces  about  the  CG  are  equal,  the  forces 
themselves  must  be  unequal,  since  their  dis- 
tances from  the  CG  are  unequal. 

The  greater  of  the  two  forces  will  be  that 
on  the  fixed  fin  area  (as  it  is  acting  nearer  to 
the  CG)  and  the  lesser  on  the  rudder. 

The  resultant  of  these  two  forces  will  be 
approximately  equal  to  their  difference  (it 
would  be  exactly  so  if  they  were  parallel) 
and  will  act  through  the  CG  in  a  direction 
approximately  parallel  to  the  greater — that  is, 
it  will  be  centripetal  (i.e.  tending  to  pull 
inwards).  Consequently  the  flight  path  be- 


98  THE  FLYER'S  GUIDE 

comes  curved  as  the  axis  of  the  machine  is 
drawn  inwards  by  this  resultant  centripetal 
force. 

The  effect  of  this  turn  is  to  produce  a 
centrifugal  force  which  balances  the  centrip- 
etal force.  The  balance  is,  of  course,  only 
exact  when  the  machine  is  correctly  banked 
for  the  turn  it  is  making. 

A  further  reference  to  the  question  of  fin 
area  is  necessary  before  the  problems  bearing 
on  a  turn  can  be  satisfactorily  mastered. 

Now,  the  arrangement  of  the  fin  area  is 
one  of  the  most  important  of  the  many 
considerations  in  aeroplane  design. 

An  aeroplane  to  be  directionally  stable  must 
fly  with  its  head  direct  to  the  relative  wind 
stream.  To  bring  about  this  condition,  the 
moment  of  pressure  on  the  fin  area  behind 
the  CG  must  be  greater  than  the  moment 
of  the  pressure  on  the  fin  area  in  front  of  the 
CG.  In  other  words,  the  centre  of  effect  of 
the  whole  fin  area  must  be  behind  the  centre 
of  gravity.  It  is  just  this  condition  that 
makes  a  good  weather-cock  always  turn  into 
the  wind. 


THE  THEORY  OF  FLIGHT  99 

Considering  our  flying  machine  again,  if 
the  centre  of  effect  of  the  fin  area  lay  in  front 
of  the  CG  it  would  always  tend  to  turn  away 
from  the  relative  wind  stream;  it  would  in 
fact  spin,  and  this  has  actually  happened 
hi  more  than  one  case. 

Well,  the  centre  of  effect  of  the  fin  area 
must  be  behind  the  CG.  That  is  one  im- 
portant axiom  with  regard  to  fin  area. 

The  next  thing  to  consider  is  whether  the 
centre  of  pressure  or  effect  of  the  fin  area 
should  be  above  or  below  the  CG.  Usually 
speaking,  it  will  be  somewhere  very  near  the 
CG,  and  hi  almost  every  case  slightly  above  it. 

If  you  consider  an  aeroplane,  there  are  a 
host  of  parts  which  constitute  fin  area,  and 
a  lot  of  these  parts,  such  as  landing  chassis 
struts  and  disc  wheels,  are  much  below  the  CG. 

The  most  usual  way  to  counteract  this  low 
fin  area  is  by  means  of  a  dihedral  angle  be- 
tween the  planes.  The  planes  thus  turned 
up  form  a  considerable  side  or  fin  area. 

To  consider  once  more  the  question  of 
turning. 

Everybody  knows  that  when  turning  a  cor- 


100  THE  FLYER'S  GUIDE 

ner  on  a  bicycle  it  is  necessary  to  lean  in- 
wards. This  is  because  there  is  a  centrifugal 
force  trying  to  pull  the  machine  outwards. 
Exactly  similarly  with  the  aeroplane.  Unless 
the  machine  is  sufficiently  banked  it  will  slip 
outwards.  If  it  is  too  much  banked  it  will 
fall  inwards.  The  exact  bank  for  any  turn 
at  any  speed  is  easily  found.  It  depends  on 
the  speed  and  the  radius  of  the  turn. 

As  soon  as  an  aeroplane  commences  to 
turn,  through  the  effect  of  forces  already  de- 
scribed, the  outside  wing  is  of  necessity  going 
faster  than  the  inside  one,  therefore  the  lift 
on  the  outside  wing  is  increased  over  that 
of  the  inside  one.  This  is  known  from  the 
fundamental  formula,  because  the  lift  varies 
as  the  square  of  the  velocity — that  is,  the 
machine  tends  to  bank.  Also,  when  a  ma- 
chine first  starts  to  turn,  until  sufficiently 
banked  it  will  slip  outwards. 

Now,  the  fact  of  the  machine  slipping  out- 
wards will  create  a  pressure  on  the  fin  area. 
If  the  centre  of  pressure  of  the  fin  area  is 
above  the  CG,  the  tendency  of  this  pressure 
will  be  to  bank  the  machine  correctly  for 


THE  THEORY  OF  FLIGHT  101 

the  turn.  If  the  centre  of  pressure  of  the 
fin  area  is  below  the  CG,  the  tendency  of 
this  pressure  will  be  to  bank  the  machine 
incorrectly  for  the  turn,  which  is  a  tendency 
to  instability.  Similarly,  if  the  machine  is 
overbanked  and  side  slips,  the  tendency  of 
the  high  fin  area  is  to  correct  it,  whereas  that 
of  the  low  one  is  to  make  it  worse. 

Imagine  next  a  machine  under  the  influence 
of  some  lateral  disturbing  force,  such  as  a 
gust. 

A  gust  striking  side  area  creates  a  pressure 
on  it.  If  the  centre  of  pressure  of  the  fin 
area  is  above  the  CG,  the  gust  will  tip  the 
machine  up  so  that  it  tends  to  turn  out  of 
the  gust,  which  is  undesirable,  while  another 
gust  coming  quickly  after  will  make  it  worse. 
On  the  other  hand,  a  low  fin  area  will  tend 
to  turn  the  machine  into  the  gust  and  to 
minimise  the  disturbing  influence. 

It  is,  therefore,  this  consideration  of  out- 
side disturbing  influences  which  keeps  the 
CP  of  the  fin  area  somewhere  near  the  CG 
and  not  too  far  above  it.  But,  on  the  other 
hand,  a  gust,  or  most  gusts,  must  be  con- 


102  THE  FLYER'S  GUIDE 

sidered  as  taking  the  machine  bodily  with  it, 
besides  being  considered  just  as  a  passing  dis- 
turbing element.  So  from  that  point  of  view 
one  would  again  be  inclined  to  argue  for  the 
higher  position  of  the  CP  of  the  fin  area.  Also 
a  gust,  as  it  passes  along,  hits  the  tail  of  the 
machine.  This  also  has  the  effect  of  turning 
the  machine  into  the  gust. 


CHAPTER  V 

INTERNAL   COMBUSTION  ENGINES 

PRACTICAL  flying  really  owes  its  birth  to 
the  development  of  the  internal  combustion 
engine.  Gliders  were  experimented  with  for 
many  years  before  the  flying  machine,  as  we 
know  it  to-day,  took  shape.  However,  power- 
driven  aeroplanes  could  not  then  be  made,  as 
all  engines  existing  at  the  time  were  far  too 
heavy. 

It  is  only  intended  to  deal  with  the  general 
principles  of  the  petrol  engine  in  this  chapter, 
as  excellent  text-books  are  provided  describ- 
ing the  various  engines  hi  detail. 

An  internal  combustion  engine  in  its  simplest 
form  consists  of  a  cylinder  which  is  bolted 
to  some  form  of  crank  case.  A  piston  works 
up  and  down  hi  the  cylinder,  and  is  con- 
nected to  a  crank  by  means  of  a  con- 
necting rod.  The  latter  has  a  bearing  at 

103 


104  THE  FLYER'S  GUIDE 

each  end.  A  pin,  called  the  gudgeon  pin, 
passes  through  this  bearing  at  the  piston 
end.  The  gudgeon  pin  is  mounted  rigidly 
in  the  piston.  Similarly  the  crank  pin  passes 
through  the  other  end  of  the  connecting  rod. 
As  the  piston  moves  up  and  down  in  the  cyl- 
inder, a  rotary  motion  is  thus  conveyed  to 
the  crank.  The  cylinder  is  fitted  with  two 
valves,  one  being  the  induction  and  the  other 
the  exhaust  valve.  A  pipe  is  fitted  over  the 
induction  valve,  through  which  gas  or  oil 
vapour  is  drawn.  The  port  of  the  exhaust 
valve  merely  leads  into  the  open. 

The  commonest  principle  upon  which  such 
engines  work  is  the  Otto  or  four-cycle  sys- 
tem, which  I  will  now  briefly  describe. 

Imagine  the  piston  at  the  top  of  its  stroke 
commencing  to  move  downwards.  As  it  moves 
downwards,  gas  or  vapour  is  drawn  into  the 
cylinder  through  the  induction  pipe.  When 
the  piston  gets  to  the  bottom  of  its  stroke, 
the  induction  valve  closes.  The  cylinder  is 
then  full  of  gas.  As  the  piston  comes  up 
it  compresses  this  gas,  there  being  no  outlet. 
When  it  gets  almost  to  the  top  of  its  stroke 


INTERNAL  COMBUSTION  ENGINES     105 

again,  the  gas  is  exploded  (usually  by  an 
electric  spark). 

The  explosion  causes  the  gas  to  expand  very 
rapidly,  which  forces  the  piston  down  again. 
When  the  piston  is  near  the  bottom,  the  ex- 
haust valve  is  mechanically  opened  and  the 
gases  commence  to  rush  out.  During  thfc 
whole  of  the  upward  stroke  the  piston  forces 
the  gases  out  of  the  cylinder.  The  cylinder 
is  then  devoid  of  gas  and  the  same  cycle  of 
operations  recurs.  The  first  stroke  is  called 
the  induction  stroke,  the  second  the  compres- 
sion, the  third  the  working,  and  the  fourth 
the  exhaust. 

Thus  only  one  stroke  in  every  four  (or  in 
two  revolutions  of  the  crank)  does  any  work. 
The  crankshaft  must  therefore  be  fitted  with 
a  sufficiently  large  flywheel  to  store  up  the 
necessary  energy  to  carry  it  over  the  other 
three  strokes  in  a  smooth  manner. 

The  construction  of  a  petrol  engine  is 
briefly  as  follows: 

The  cylinder  (or  cylinders)  are  usually  made 
of  cast  iron  (sometimes  steel).  The  inside, 
or  bore  of  the  cylinder  is  cast  slightly  smaller 


106  THE  FLYER'S  GUIDE 

than  the  required  dimension.  This  allows 
for  it  to  be  machined  to  size.  As  cast  iron 
leaves  a  rough  surface,  the  inside  of  a  cyl- 
inder has  to  be  bored  smooth  and  true. 
The  outside  wall  of  the  cylinder  varies  accord- 
ing to  whether  it  is  to  be  air  or  water  cooled. 
In  the  former  case  the  outside  of  the  cylinder 
is  cast  in  fins,  which  radiate  off  the  heat.  If 
a  system  of  water  cooling  is  to  be  adopted, 
the  cylinder  has  to  be  cast  with  a  jacket 
round  it,  in  which  the  water  can  circulate. 
In  neither  case  does  the  outside  of  the  cyl- 
inder require  machining.  Cylinder  walls  have 
to  be  of  sufficient  thickness,  both  to  ensure 
of  their  standing  up  against  the  internal 
pressure  and  of  avoiding  blow-holes  (blow- 
holes are  very  common  in  iron  castings). 
Cylinders  have  to  be  provided  with  valve 
seatings,  which  may  either  be  accommodated 
in  the  cylinder  head  or  in  special  valve 
pockets.  In  any  case  valve  seatings  have  to 
be  very  carefully  machined.  Cylinders  may 
either  be  cast  in  one  or  two  pieces.  In  the 
latter  event,  the  cylinder  head  is  bolted  on 
to  the  cylinder  itself.  The  cylinder  is  at- 


INTERNAL  COMBUSTION  ENGINES    107 

tached  (usually  by  bolts  or  studs)  to  a  crank 
case.  The  latter  will  generally  be  cast  alu- 
minium. 

In  some  aeronautical  engines  steel  is  used 
for  both  cylinders  and  crank  case. 

A  crankshaft  (usually  a  steel  forging)  re- 
volves about  bearings  hi  the  ends  of  the 
crank  case. 

Pistons  are  almost  invariably  made  of  cast 
iron.  Connecting  rods,  which  are  usually 
steel  forgings,  are  fitted  with  bearings  (such 
as  phosphor-bronze)  at  each  end.  The  small 
end  bearing  works  about  the  gudgeon  pin 
and  the  big  end  about  the  crank  pin.  Many 
big  ends  are  now  fitted  with  ball-bearings  in 
order  to  reduce  friction,  and  thus  obtain  a 
maximum  efficiency.  Pistons  are  fitted  with 
cast  iron  split  rings  (usually  three  or  four) 
to  prevent  the  gas  leaking  past  into  the 
crank  case. 

Induction  valves  may  be  either  automatic 
or  mechanical.  In  the  former  case  a  short 
stem  valve,  free  to  work  up  and  down  in  its 
guide,  is  kept  on  its  seating  by  a  spring 
(comparatively  light  spring).  As  the  piston 


108  THE  FLYER'S  GUIDE 

/ 

goes  down,  the  partial  vacuum  created  over- 
comes the  spring  (if  light  enough)  and  the 
valve  opens.  The  oil  vapour  from  the  car- 
burettor then  rushes  into  the  cylinder  head 
above  the  piston.  As  the  piston  comes  up 
on  the  compression  stroke  the  pressure  forces 
the  valve  to  shut.  The  pressure  in  the  cyl- 
inder is  sufficient  to  keep  the  valve  closed 
until  the  induction  stroke  comes  round  again. 
Mechanically  operated  induction  valves  are 
fitted  with  stronger  springs  which  would  not 
allow  of  the  valve  being  opened  by  suction. 
As  their  name  suggests,  they  are  dependent 
for  their  opening  on  a  device  worked  by  the 
engine.  As  already  explained,  the  induction 
valve  is  only  required  to' be  open  during  one 
stroke  of  every  four — that  is,  in  two  revo- 
lutions of  the  crankshaft. 

The  simplest  form  of  mechanical  valve  is 
worked  as  follows.  The  valve  works  in  a 
seating  in  a  valve  pocket  and  has  a  stem 
about  7  inches  long.  The  valve  pocket, 
which  is  part  of  the  cylinder  casting,  projects 
over  one  side  of  the  cylinder.  The  valve 
stem  passes  through  a  guide  in  the  pocket 


INTERNAL  COMBUSTION  ENGINES    109 

and  assumes  an  upright  position  parallel  to 
the  cylinder  walls.  The  valve  head  is  kept 
on  its  seating  by  means  of  a  strong  spring 
passed  over  this  guide.  The  spring  is  kept 
in  compression  by  means  of  a  washer  pin  and 
passed  through  the  stem.  A  push  rod  is 
mounted  underneath  the  valve  stem  and  is 
actuated  by  a  cam.  A  cam  is  a  circular  steel 
disc  (case  hardened)  with  a  lump  on  it  and 
is  mounted  on  a  camshaft,  which  revolves  at 
half  the  speed  of  the  crankshaft.  The  lower 
end  of  the  push  rod,  which  is  usually  fitted 
with  a  roller  (case-hardened  steel),  rests  on 
the  circumference  of  the  cam.  The  push 
rod,  of  course,  is  mounted  in  a  guide  so  that 
it  can  only  travel  up  and  down.  As  the  lump 
on  the  cam  comes  round  under  the  push  rod 
the  latter  is  forced  up.  The  push  rod  hi  its 
turn  forces  the  valve  open.  The  fact  of  the 
cam  revolving  only  half  the  speed  of  the 
crankshaft  makes  the  valve  open  only  once 
in  two  revolutions  of  the  latter.  As  soon  as 
the  lump  on  the  cam  has  passed  from  under- 
neath the  push  rod  the  valve  is  forced  shut 
again  by  its  spring. 


110  THE  FLYER'S  GUIDE 

There  are  many  modifications  of  this  sys- 
tem in  practice,  some  valves  being  overhead, 
in  which  case  they  are  operated  by  tappet 
rods  and  rockers,  or  by  rockers  only  from  an 
overhead  camshaft.  The  operation  of  ex- 
haust valves  is  exactly  similar  to  that  of 
mechanical  induction  valves. 

The  exact  setting  of  valves  varies  on 
different  engines,  but  a  rough  guide  is  as 
under. 

The  induction  valve  should  open  very  soon 
after  the  piston  is  past  its  top  dead  centre 
(about  6  degrees)  and  remain  open  during  the 
whole  of  the  suction  stroke.  As  soon  as  the  pis- 
ton has  passed  the  bottom  dead  centre  and 
commenced  to  come  up  to  compress  the  charge, 
the  induction  valve  should  close.  In  prac- 
tice it  will  usually  close  about  6  degrees  after 
the  piston  has  passed  bottom  dead  centre. 
Both  valves  remain  closed  during  the  com- 
pression stroke  and  during  the  commence- 
ment of  the  firing  stroke.  It  is,  however, 
advantageous  for  the  exhaust  valve  to  be 
timed  to  open  well  before  the  piston  reaches 
the  bottom  dead  centre  (probably  about  50  de- 


INTERNAL  COMBUSTION  ENGINES    111 

grees) .  The  expansion  of  gas  during  the  firing 
stroke  is  so  rapid  that,  providing  the  spark 
is  sufficiently  advanced,  most  of  the  useful 
work  has  been  done  on  the  piston  by  the 
time  it  has  got  half  way  down  its  stroke.  An 
early  opening  of  the  exhaust  valve  then  en- 
sures an  effective  escape  of  the  burnt  gases 
and  consequent  absence  of  pressure  against 
the  piston  on  its  return  stroke.  The  exhaust 
valve  should  be  timed  to  close  when  the 
piston  reaches  top  dead  centre  again. 

The  spark  must  be  timed  so  as  to  occur 
well  before  the  piston  reaches  the  top  of  its 
compression  stroke.  It  must  be  borne  in 
mind  that  the  explosion  of  the  charge  is  not 
instantaneous.  By  firing  the  charge  before 
the  piston  reaches  the  top  of  its  stroke  the 
full  force  of  the  explosion  is  felt  by  the 
time  the  piston  begins  to  go  down  again. 
If  the  spark  were  timed  to  occur  at  the 
moment  the  piston  was  at  the  top,  the  full 
force  of  the  explosion  would  not  be  felt  until 
the  piston  was  well  on  its  way  down,  and  a 
great  deal  of  efficiency  would  be  lost.  When 
fully  advanced,  the  spark  should  occur  about 


112  THE  FLYER'S  GUIDE 

25  degrees  before  the  piston  reaches  top 
dead  centre. 

The  next  consideration  is  the  requisite  sup- 
ply of  petrol  vapour  to  the  engine.  Petrol 
is  vapourised  in  a  carburettor,  which  in  its 
simplest  form  consists  of  two  parts:  (1) 
float  chamber,  (2)  jet  or  vapourising  chamber. 

Petrol  flows  from  the  tank  into  the  bottom 
of  the  float  chamber  either  by  gravity  or  by 
pressure.  The  supply  is  regulated  by  means 
of  a  float.  As  the  latter  rises  with  the  in- 
coming petrol,  it  forces  a  needle  valve  down, 
which  checks  the  flow.  As  the  petrol  is 
drawn  through  the  jet  from  the  float  cham- 
ber, the  float  falls,  thus  releasing  the  needle 
valve.  A  small  pipe  leads  from  the  bottom 
of  the  float  chamber,  making  a  free  passage 
for  the  petrol  up  the  centre  of  the  jet.  The 
top  of  the  jet  should  be  the  same  level  as 
the  petrol  in  the  float  chamber  when  the  latter 
is  full.  As  explained,  the  jet  is  situated  in 
the  vapourising  chamber,  to  the  top  of  which 
the  induction  pipe  is  attached.  Holes  are 
fitted  in  the  jet  chamber  below  the  jet  through 
which  air  is  drawn.  Extra  air  holes  or  an  air 


INTERNAL  COMBUSTION  ENGINES    113 

valve  (or  both)  may  be  fitted  on  the  induc- 
tion pipe  above  the  jet. 

As  the  piston  comes  down  on  the  induc- 
tion stroke,  a  partial  vacuum  is  created  in 
the  induction  pipe.  This  causes  petrol  to 
be  drawn  through  the  jet  from  the  float 
chamber.  The  orifice  in  the  jet  being  very 
small  (it  varies  according  to  the  size  of  the 
engine),  the  petrol  when  drawn  through 
squirts  out  in  very  fine  columns.  Air  is  at 
the  same  time  drawn  through  the  holes  in 
the  bottom  of  the  jet  chamber.  The  petrol, 
being  very  volatile,  evaporates  and  forms  an 
explosive  mixture  with  the  air.  The  correct 
proportion  of  petrol  vapour  to  air  by  volumes 
is  about  1  to  16. 

Diagram  Q  is  a  rough  sketch  of  a  simple 
carburettor.  It  does  not  represent  any  par- 
ticular design.  It  is  a  section  taken  through 
the  centre  of  the  carburettor. 

It  must  be  remembered  that  the  working 
parts  of  an  engine  are  revolving  (or  moving) 
at  very  high  speeds,  consequently  the  friction 
between  such  parts  is  great,  which  necessi- 
tates a  very  efficient  system  of  lubrication. 


114 


THE  FLYER'S  GUIDE 


Bearings  are  lubricated  by  a  thin  film  of 
oil  being  formed  between  the  bearing  and  the 
moving  surface.  It  is  essential  that  all  bear- 


DIAGRAM  Q. 

A,  Screw  thread  to  take  petrol  pipe  union;  B,  Needle  valve;  C,  Collar 
actuated  by  balance  weights;  D,  Fulcrum;  E,  Balance  weights; 
F,  Float  chamber;  F1,  Top  of  Float  chamber;  G,  Float;  H,  Jet 
screwed  on  to  (I)  pipe  leading  from  Float  chamber;  J,  Air  hole; 
K,  Choke  tube;  L,  Throttle  actuated  by  outside  lever;  M,  Screw 
thread  to  take  induction  pipe  union. 


INTERNAL  COMBUSTION  ENGINES    115 

ings  should  be  truly  aligned  and  worked  to 
a  smooth  surface  for  lubrication  to  be  effect- 
ive. The  film  of  oil  is  formed  by  the  relative 
motion  of  the  two  surfaces,  and  the  higher 
the  relative  velocity  and  the  more  viscous  the 
oil,  the  more  stable  will  the  film  become. 

At  low  speeds,  especially  under  heavy  loads, 
the  oil  film  is  liable  to  be  squashed  from  be- 
tween the  bearing  surfaces,  and  the  lubrica- 
tion will  then  entirely  depend  on  the  greasi- 
ness  of  the  oily  surfaces;  for  this  reason 
slow  moving  toothed  wheels  are  better  lubri- 
cated by  a  thick  grease  than  any  sort  of  oil. 

At  high  speeds  the  film  of  oil  will  form 
between  the  moving  surfaces  even  if  the  oil 
is  fairly  thin,  and,  as  far  as  friction  and 
consequent  heating  are  concerned,  the  thin- 
ner the  oil  the  better. 

Animal  and  vegetable  oils  are  more  greasy 
than  mineral  oils,  but,  on  the  other  hand, 
they  soon  become  acid  and  gummy  and  car- 
bonise very  quickly  when  in  contact  with 
hot  cylinder  walls;  therefore  mineral  oils  are 
almost  invariably  used  for  lubricating  internal 
combustion  engines.  Rotary  aero  engines 


116  THE  FLYER'S   GUIDE 

form  an  exception,  as  castor  oil  is  always  used. 
In  most  cases  it  should,  however,  be  borne  in 
mind  that  fresh  oil  is  always  being  employed, 
the  oil  being  pumped  right  out  of  the  engine 
through  the  exhaust  valves,  whereas  stationary 
engines,  which  use  mineral  oil,  have  a  very 
much  lower  oil  consumption,  the  same  oil, 
after  being  pumped  through  the  bearings, 
etc.,  being  filtered  in  the  crank  case  and  used 
again  and  again. 

In  practically  every  aeroplane  engine  the 
oil  is  forced  through  to  the  bearings,  etc.,  by 
means  of  a  force  pump.  In  many  cases,  how- 
ever, the  centrifugal  force  created  by  the 
crank  (or  connecting  rods  in  the  case  of  rotary 
engines)  is  utilised  to  distribute  the  oil  to 
cylinder  walls,  small  end  bearings,  etc. 

From  the  foregoing  it  should  be  realized 
that  four  essential  conditions  have  to  be 
fulfilled  in  order  that  a  petrol  motor  may 
start  and  keep  running.  They  are: 

(1)  An  explosive  mixture  of  the  correct 
strength  has  to  be  drawn  into  the 
cylinder. 


INTERNAL  COMBUSTION  ENGINES    117 

(2)  This   mixture   must    be    sufficiently 

compressed  to  ensure  efficient  ex- 
plosion. 

(3)  Some  method  of  igniting  the  charge  at 

the  right  time  must  be  provided. 

(4)  All  working  parts  must  be  properly 

lubricated. 

The  peculiarities  and  more  common  troubles 
associated  with  the  above  axioms  may  be 
set  out  as  follows: 

(1)  This  depends  on : 

(a)  The  petrol  supply  to  the  carburettor 
working  properly.     A  kinked,  leaky,  or  dirty 
petrol  pipe  will  interrupt  the  even  flow  of 
the  petrol. 

(b)  The  correct  carburettor  and  jet  for  the 
engine  must  be  used.    All  parts  of  the  car- 
burettor must  be  thoroughly  clean  and  free 
from  grit  and  dirt. 

(c)  The  induction  valve  must  be  working 
properly  (and  correctly  timed  in  the  case  of 
mechanically  operated  valves). 

(d)  In  the  case  of  a  multi-cylinder  engine  a 
suitable  arrangement  of  induction  pipes  is 


118  THE  FLYER'S  GUIDE 

most  necessary.  In  the  case  of  a  four-cyl- 
inder engine,  for  example,  it  is  inadvisable  to 
have  the  carburettor  at  one  end  feeding  all 
four  cylinders  from  a  single  pipe.  In  that 
event  the  cylinders  nearest  to  the  carburettor 
are  inclined  to  starve  the  others.  It  would 
be  better  in  such  a  case  to  have  the  car- 
burettor between  the  two  centre  cylinders 
with  the  induction  pipes  leading  from  it  (one 
for  each  pair  of  cylinders). 

(2)  Sufficient  compression  can  only  be  en- 
sured by  guarding  against  the  leakage  of  gas 
either  past  the  pistons  or  through  the  valves. 

As  already  mentioned,  piston  rings  are 
fitted  to  prevent  leakage  past  the  piston. 
Piston  rings,  which  are  of  cast  iron,  are  turned 
just  a  shade  larger  diameter  than  that  of 
the  cylinder.  A  section  is  then  cut  out  to 
enable  the  ring  to  be  inserted  in  the  cylinder. 
Each  ring  fits  in  a  groove  in  the  piston,  and 
its  natural  spring  tends  to  keep  it  pressed 
out  against  the  cylinder  wall.  Each  ring  is 
fitted  so  as  to  leave  a  small  clearance,  thus 
allowing  for  the  expansion  of  the  ring  under 
heat.  When  fitting  the  "rings  to  a  piston,  the 


INTERNAL  COMBUSTION  ENGINES    119 

cuts  in  the  former  must  not  be  superimposed, 
because  the  clearance  allows  of  a  slight  leakage. 

Valves  constantly  cause  a  loss  of  com- 
pression owing  to  the  high  temperatures  to 
which  they  are  exposed,  either  the  valve 
head  or  its  seating  becoming  pitted  through 
dirt  (little  pieces  of  carbon)  getting  between 
them. 

To  keep  a  good  seating,  valves  have  to  be 
constantly  reground.  It  is  not  uncommon  for 
valves  to  stick  open.  To  avoid  this  trouble 
valve  stems  must  be  kept  clean  and  free  from 
any  gumminess.  Valve  springs  must  also  be 
carefully  watched,  as  in  tune  they  either  break 
or  lose  their  strength. 

In  the  case  of  all  mechanical  valves  (either 
induction  or  exhaust)  it  is  essential  that  there 
should  be  a  small  clearance  between  the  valve 
stem  and  push  rod  (or  rocking  bar)  when  the 
valve  is  shut  and  the  engine  cold.  If  no 
such  clearance  is  fitted,  both  the  push  rod 
and  valve  stem  expanding  under  heat  will 
prevent  the  valve  from  shutting  properly. 
A  great  loss  of  compression  would  ensue 
thereform. 


120  THE  FLYER'S  GUIDE 

(3)  It  has  already  been  briefly  explained 
why  the  ignition  has  to  be  timed  so  that  the 
spark  may  occur  before  the  piston  gets  to 
top  dead  centre.  Some  of  the  chief  points 
to  look  to  with  regard  to  ignition  are: 

(a)  See  that  the  platinum  points  on  the 
make  and  break  are  properly  adjusted  and 
that  they  are  not  burnt.  If  burnt  at  all, 
the  surfaces  would  be  rough. 

Platinum  points  can  be  trued  up  with  a 
very  fine  file  so  as  to  ensure  good  smooth 
surfaces  of  contact. 

(6)  The  distributor  of  an  aeroplane  engine 
will  require  constantly  cleaning  with  petrol, 
as  in  almost  every  engine  considerable  quan- 
tities of  oil  are  thrown  out  on  to  it.  Oil  on 
the  distributor  prevents  the  brush  making 
good  contact. 

(c)  Sparking  plugs  are  a  considerable  source 
of  trouble.  They  require  constant  cleaning 
and  not  infrequently  renewing.  Oil  between 
the  points  becomes  burnt  and  makes  a  direct 
path  for  the  current,  and  consequently  no 
spark  is  produced.  Porcelains  are  occasionally 
fractured  by  vibration,  in  which  case  a  new 


INTERNAL  COMBUSTION  ENGINES    121 

plug  must  be  substituted  for  the  broken 
one. 

(d)  Care  must  be  taken  to  see  that  there 
is  no  short  circuit  in  the  wiring.  A  wire 
passing  very  near  an  exhaust  pipe  will  very 
likely  short-circuit  owing  to  the  insulation 
being  burnt  off. 

(4)  Lubrication  troubles  are  usually  caused 
by: 

(a)  Lack  of  oil.  Great  care  must  be  taken 
to  see  that  all  machines  are  filled  with  suf- 
ficient oil  to  outlast  the  petrol. 

Some  engines  (such  as  the  Gnome)  are 
fitted  with  an  external  oil  tank  and  pump. 
In  such  cases  the  oil  pipes  must  receive  con- 
stant attention.  The  vibration  constantly 
causes  oil  pipes  to  fracture.  Particular  care 
must  be  taken  to  see  that  the  tap  is  always 
turned  open.  It  is  a  very  good  plan  to  keep 
oil  taps  permanently  fixed  in  the  open  po- 
sition. 

In  engines  (such  as  the  Renault)  where 
the  oil  is  poured  straight  into  the  sump, 
attention  must  be  given  to  the  regular  drain- 
ing of  the  latter. 


122  THE  FLYER'S  GUIDE 

(6)  The  quality  of  oil  as  recommended  for 
the  particular  engine  must  only  be  used. 

(c)  The  cold  weather  causes  oil  to  become 
very  thick.  In  winter  castor  oil  may  be 
mixed  with  a  little  methylated  spirits  to 
thin  it  out  (about  one  part  of  methylated 
spirits  to  eight  of  castor  oil  by  volume). 
Similarly  the  thick  air-cooled  mineral  oils 
may  be  mixed  with  a  small  quantity  of  a 
thinner  quality. 

Before  proceeding  further  it  may  be  as 
well  to  explain  two  terms  which  are  fre- 
quently confused — namely,  backfiring  and  pre- 
ignition. 

Backfiring  occurs  when  the  charge  explodes 
on  entering  the  cylinder  through  the  open 
induction  valve  and  back  into  the  carburet- 
tor, which  is  then  liable  to  catch  fire. 

The  causes  of  backfiring  are: 

(a)  Through  the  mixture  being  too  weak. 
The  immediate  cause  of  this  is  probably  due 
to  the  very  slow  explosion  of  the  previous 
charge  keeping  the  piston  head  at  a  high 
temperature,  thus  setting  the  new  charge  alight 
immediately  it  enters  the  cylinder  head. 


INTERNAL  COMBUSTION  ENGINES    123 

(6)  Carbon  deposits  being  formed  on  the 
piston  head  and  cylinder  walls  becoming  heated 
to  incandescence,  thus  igniting  the  incoming 
charge  immediately  on  contact. 

(c)  A  leaky  exhaust  valve  will  allow  the 
hot  exhaust  gases  to  be  sucked  back  from 
the   exhaust   pipe   and   so    explode   the   in- 
coming charge. 

(d)  An  inlet  valve,  which  becomes  broken 
or  hung  up,  will,  of  course,  allow  the  charge 
on  being  exploded  in  the  cylinder  head  to 
blow  back  into  the  carburettor. 

Backfiring  is  very  dangerous,  as,  once  the 
carburettor  has  caught  alight,  the  fire  will 
spread  very  rapidly,  especially  in  an  aeroplane 
where  it  is  fanned  by  a  constant  flow  of  air. 

Wire  gauze  is  now  usually  fitted  to  induc- 
tion pipes.  This  has  the  effect  of  preventing 
a  blow  back  (backfire)  reaching  the  car- 
burettor. 

Preignition  occurs  when  the  charge  is  fired 
too  early  on  the  compression  stroke,  thereby 
tending  to  make  the  engine  run  backwards. 
This  may  be  caused  by: 

(a)  The  spark  being  too  far  advanced,  thus 


124  THE  FLYER'S  GUIDE 

causing  the  expansion  of  the  gas  to  be  too 
rapid  in  comparison  with  the  position  of  the 
piston.  Great  care  should  be  taken  when 
starting  an  engine  by  hand  to  have  the 
spark  retarded,  as  the  rapid  backward  mo- 
tion caused  by  preignition  is  sufficient  to 
break  a  wrist  (or  worse). 

(6)  Overheating,  which  may  be  caused  by  a 
defective  water  circulation,  by  insufficient  lu- 
brication, or  by  the  spark  being  too  far  re- 
tarded. If  the  spark  is  too  far  retarded, 
the  full  force  of  the  explosion  is  not  felt 
until  the  piston  is  well  on  its  way  down  its 
stroke.  Thus  a  large  area  of  the  cylinder  wall 
becomes  exposed  to  the  maximum  heat  of 
explosion. 

Carbon  deposits  on  the  piston  head  and 
cylinder  walls  (caused  by  too  rich  a  mixture) 
also  cause  overheating  (as  explained  above). 

A  few  notes  on  indicator  diagrams  may  be 
of  assistance  in  mastering  the  principles  of 
the  internal  combustion  engine. 

An  indicator  diagram  is  a  graph  showing 
the  pressure  in  the  cylinder  at  all  points  in 
the  stroke  of  the  piston  during  the  whole 


INTERNAL  COMBUSTION  ENGINES    125 

cycle  of  operations  (that  is  four  strokes). 
The  pressures  are  actually  taken  in  practice 
by  means  of  an  indicator. 

Diagram  R  represents  a  typical  curve  dur- 
ing the  four  strokes  of  one  piston  of  an  en- 
gine. The  ordinate  erected  at  A  represents 
the  top  of  the  stroke,  and  that  at  B  the 
bottom. 

Consider  first  the  induction  stroke,  which 
is  represented  by  a!  bi.  Now  the  charge 
enters  the  cylinder,  where  the  pressure  is 
slightly  below  atmosperhic  (owing  to  the  par- 
tial vacuum  created  by  the  descending  piston), 
with  a  rush  and  does  work  on  the  piston. 

Now  the  work  done  (either  on  or  against 
the  piston)  during  any  stroke  is  represented 
on  the  graph  by  the  area  bounded  by  (1) 
the  pressure  curve  for  that  stroke,  (2)  the 
ordinate  through  A,  (3)  the  ordinate  through 
B,  (4)  the  base  line  of  no  pressure — that  is, 
the  work  done  on  the  piston  during  the  in- 
duction stroke  is  represented  by  the  area 
ai  bi,  B  A. 

As  soon  as  the  piston  turns  to  come  up  on 
compression  the  pressure  rises  very  quickly. 


126  THE  FLYER'S  GUIDE 

The  portion  of  the  curve  bi  a2  represents  the 
pressures  throughout  the  compression  stroke. 
The  work  done  against  the  piston  is  therefore 
represented  by  the  figure  A  a2  bi  B. 

In  this  diagram  it  is  assumed  that  the 
spark  takes  place  when  the  piston  is  just  at 
the  top  of  the  stroke.  The  diagram  shows 
clearly  that  the  spark  is  then  too  far  re- 
tarded, as  the  maximum  pressure  does  not 
occur  until  the  piston  is  well  on  its  way 
down. 

The  firing  stroke  is  then  represented  by  the 
portion  of  the  curve  a2b2.  As  the  piston 
gets  towards  the  bottom  of  its  stroke  the 
pressure  falls  rapidly.  This  is  accentuated 
by  an  early  opening  of  the  exhaust  valve. 
The  useful  work  done  on  the  piston  during 
the  firing  stroke  then  is  represented  by  the 
figure  A  a2  b2  B. 

During  the  exhaust  stroke  the  pressure  in 
the  cylinder  will  be  working  against  the  piston. 
If  the  exhaust  valve  is  properly  timed  and 
is  sufficiently  large,  this  pressure  should  only 
be  very  slight  until  when  the  piston  reaches 
the  top  it  becomes  equal  to  zero.  The  work 


INTERNAL  COMBUSTION  ENGINES    127 

done  against  the  piston  during  this  stroke 
is  then  represented  by  the  figure  A  a1  b2  B. 

The  total  useful  work  done  during  the  four 
strokes  can  then  be  found  by  subtracting  the 
work  done  against  the  piston  from  the  work 
done  on  the  piston. 

Considering  the  diagram  again.  The  por- 
tions of  the  curve  representing  the  exhaust 
stroke  and  the  induction  stroke  are  very 
near  together.  The  difference  between  the 
areas  A  a1  b2  B  and  A  a1  b1  B  (that  is,  the 
small  area  enclosed  by  the  curves)  gives  the 
net  work  done  against  the  piston  during  these 
two  strokes.  As  can  be  seen  from  the  dia- 
gram, this  area  is  very  small. 

In  a  similar  way  it  is  clear  that  the  figure 
bounded  by  the  curves  of  the  compression  and 
firing  strokes  gives  the  net  useful  work  done 
on  the  piston  during  these  two  strokes. 
Therefore,  it  is  clear  that  the  net  useful 
work  done  on  the  piston  during  the  whole 
four  strokes  is  equal  to  the  area  bounded  by 
the  compression-firing  stroke  curves  minus  the 
area  bounded  by  the  exhaust-induction  stroke 
curves.  The  latter  being  almost  negligible, 


128 


THE  FLYER'S  GUIDE 


the  total  useful  "work  done  on  the  piston  may 
be  assumed  to  be  represented  by  the  figure 
between  the  compression-firing  stroke  curves. 


Pressures 


-Length  of  Stroke 

DIAGRAM  R. 
(This  Diagram  is  not  to  Scale) 

If  a  number  of  ordinates  (not  less  than 
about  10)  are  erected  between  these  two 
portions  of  the  curve,  the  mean  of  them 
may  be  taken  as  the  mean  pressure  in  the 
cylinder  during  the  four  strokes  (that  is,  in 
one  complete  cycle  of  operations)  and  is 


INTERNAL  COMBUSTION  ENGINES    129 

expressed  in  Ibs.  per  square  inch  (if  using 
British  units). 

A  formula  giving  indicated  horse-power  may 
now  be  deduced  from  the  above  diagram. 

Assuming  that  the  engine  in  question  has 
only  one  cylinder,  and  that  the  area  of  the 
piston  is  A  square  inches.  The  mean  pres- 
sure per  unit  area  already  found  from  the 
diagram  will  be  called  P  Ibs.  per  square 
inch.  The  total  pressure  on  the  piston  then 
=  P  X  A  Ibs.  per  cycle. 

If  L  be  the  length  of  the  piston's  stroke  in 
feet,  the  work  done  per  cycle  =  PAL  foot-lbs. 

If  N  be  the  number  of  revolutions  per 

N 

minute,  there  will  be  -~-  explosions  per  min- 
ute. Then  the  work  done  per  minute  (that 
is,  the  power)  will  be: 

PLAN- 

— s —  foot-lbs.  per  minute. 
2t 

Since  1  horse-power  =  33,000  foot-lbs.  per 
minute,  then  the  indicated  horse-power 

-    PLAN        PLAN 


2X33,000     66,000' 


130  THE  FLYER'S  GUIDE 

Now,  the  petrol  engine  is  simply  a  heat  en- 
gine. The  source  of  the  heat  supplied  is  the 
fuel,  each  pound  of  which  gives  out  a  certain 
definite  amount  of  heat  when  burnt. 

This  heat  is  dissipated  in  four  ways: 

(1)  Part  does  useful  work  on  the  piston; 

(2)  Part  escapes  with  the  exhaust  gases 

at  the  end  of  the  stroke; 

(3)  Part  goes  into  the  cooling  system; 

(4)  Part,  but  only  a  very  small  part,  is 

lost  by  radiation,  and  may  be  neg- 
lected. 

Considering  the  loss  under  heading  (2). 
The  only  way  to  lessen  this  loss  is  by  re- 
ducing the  temperature  of  the  gases  before 
they  leave  the  cylinders. 

Now,  at  the  end  of  the  explosion  there  is 
always  a  certain  definite  amount  of  heat 
present  in  the  burnt  gases.  During  expan- 
sion these  gases  do  work,  and  lose  an  amount 
of  heat  corresponding  to  the  amount  of  work 
done  by  them  on  the  pistons.  Hence  by 
making  them  do  the  maximum  amount  of 
work  on  the  piston,  these  gases  will  be  re- 


INTERNAL  COMBUSTION  ENGINES    131 

duced  to  a  minimum  temperature.  To  make 
them  do  work  they  must  be  expanded;  and 
to  get  the  maximum  amount  of  work  out  of 
them,  they  must  be  expanded  as  much  as 
possible.  The  travel  of  the  piston  is  the 
same  on  the  compression  as  on  the  working 
stroke,  and  so  the  maximum  ratio  of  ex- 
pansion is  practically  the  same  as  the  ratio 
of  compression.  If  the  latter  be  made  too 
great,  however,  the  heat  generated  in  the 
unexploded  mixture  during  compression  will 
be  so  great  that  it  will  cause  preignition, 
and  loss  of  power  will  ensue.  Therefore,  the 
degree  of  compression  and  hence  the  ratio  of 
expansion  of  the  gases  is  limited. 

To  obtain  the  maximum  benefit  of  the 
ratio  of  expansion  the  gases  should  be  just, 
and  only  just,  completely  burnt  at  the  in- 
stant the  piston  starts  on  its  working  stroke. 
As  already  explained,  the  spark  must  be 
advanced  so  as  to  occur  while  the  piston  is 
still  going  up  on  the  compression  stroke. 
When  the  engine  is  running  fast  the  spark 
requires  to  be  more  advanced  than  when 
running  slow,  because  the  speed  of  the  piston 


132  THE  FLYER'S  GUIDE 

is  greater  in  the  former  case  while  the  time 
occupied  by  combustion  remains  approxi- 
mately the  same. 

Considering  the  losses  under  heading  (3), 
the  amount  of  heat  passing  out  to  the  cooling 
system  will  depend  on: 

(a)  The  temperature  of  the  burnt  gases; 
(6)  The  area  of  cylinder  walls   exposed 

to  these  gases; 
(c)  The  time  these  gases  are  in  contact 

with  these  walls. 

(a)  The  temperature  of  the  gases  cannot 
be  lowered  without  impairing  the  efficiency 
of  the  engine,  as  explained  above. 

(6)  The  loss  of  heat  can  be  reduced  to  a 
minimum  by  arranging  that  the  explosion  is 
just  completed  when  the  area  of  cylinder  walls 
exposed  is  a  minimum — that  is,  when  the 
piston  is  at  the  top  of  its  stroke.  This  is 
also  the  condition,  already  explained,  to  ob- 
tain the  maximum  ratio  of  expansion. 

(c)  The  time  the  gases  are  in  contact  with 
the  cylinder  walls  is  dependent  on  the  rate 
of  explosion.  To  reduce  the  time  taken  to 


INTERNAL  COMBUSTION  ENGINES    133 

complete  combustion  the  mixture  must  be 
of  the  correct  strength  and  undiluted  with 
burnt  gases  remaining  over  from  the  previous 
cycle.  To  prevent  burnt  gases  remaining 
in  the  cylinder,  the  exhaust  valve  must  be 


Pressures 


-Lenyt/i  of  Strate 

DIAGRAM  S. 
(This  Diagram  is  not  to  Scale.) 

sufficiently  large,  must  have  sufficient  lift, 
and  must  be  correctly  timed. 

Diagram  S  is  an  indicator  diagram,*$imilar 
to  diagram  R,  except  that  the  spark  is  cor- 
rectly advanced,  so  that  the  explosion  is 
complete  by  the  time  the  piston  gets  to  the 


134  THE  FLYER'S  GUIDE 

top  of  the  compression  stroke.  The  diagram 
should  be  self-explanatory,  the  extra  amount 
of  work  done  on  the  piston  being  apparent 
from  the  figures. 

When  working  on  petrol  engines  it  must 
be  borne  in  mind  that  all  the  parts  are  very 
light  and  delicate  (this  particularly  applies  to 
aeroplane  engines,  where  every  ounce  of 
weight  has  to  be  saved).  Particular  care 
must  be  taken  in  handling  all  parts  and  the 
correct  kind  of  tools  must  be  invariably 
used.  Most  engines  are  supplied  with  special 
tools,  and  these  must  always  be  used.  Clean- 
liness and  absence  of  dust  and  grit  are  es- 
sential when  doing  any  work  on  an  engine. 


CHAPTER  VI 

IGNITION   DEVICES 

IT  would  appear  fitting  to  commence  this 
chapter  with  a  few  notes  on  electro-mag- 
netic induction.  Consider  an  electric  cur- 
rent passing  through  any  conductor  (e.g.  a 
piece  of  wire);  as  soon  as  the  current  com- 
mences to  flow,  a  magnetic  field  is  created 
about  that  conductor  from  which  the  lines 
of  force  move  out  radially.  Assuming  one 
conductor  to  be  a  coil  of  insulated  wire  form- 
ing part  of  a  closed  circuit.  Now  wind 
another  length  of  insulated  wire  around  the 
original  conductor.  As  soon  as  the  current 
is  switched  on  to  pass  through  the  latter,  the 
lines  of  force  thus  created  in  radiating  out- 
wards cut  the  former  and  set  up  a  momentary 
DP  (difference  of  potential)  in  it,  which  is 
easily  detected  by  means  of  a  galvanometer. 
The  current  thus  created  is  called  an  in- 
duced current,  and  only  lasts  for  the  instant 

135 


136  THE  FLYER'S  GUIDE 

that  the  lines  of  force  from  the  original  con- 
ductor actually  cut  it.  In  future,  reference 
will  be  made  to  the  original  conductor  as 
the  primary  circuit  or  winding  and  to  the 
outside  coil  as  the  secondary.  As  soon  as 
the  current  is  switched  off  in  the  primary  cir- 
cuit, the  magnetic  field  is  discharged  and 
the  lines  of  force  radiate  inwards  and  so 
again  cut  the  secondary  winding  in  which  a 
DP  is  again  created.  In  this  case,  however, 
the  direction  of  the  induced  current  will  be 
opposite  to  that  created  by  switching  on 
the  current  in  the  primary  circuit. 

The  foregoing  then  briefly  explains  the 
origin  of  an  induced  current. 

The  voltage  produced  in  the  secondary 
circuit  is  dependent  on  the  rate  at  which 
it  is  cut  by  the  lines  of  force — that  is,  the 
number  of  lines  of  force  divided  by  the  time 
they  take  to  cut  it.  If  this  rate  is  sufficiently 
high,  a  very  high  voltage  can  be  produced 
in  the  secondary  circuit.  To  bring  about 
such  a  result  the  following  arrangements  are 
adopted: 

(1)  The  primary  circuit  is  wound  in  the 


IGNITION  DEVICES  137 

form  of  a  hollow  cylinder,  the  length  of  con- 
ductor emitting  lines  of  force  being  thereby 
increased. 

(2)  An    iron    core    is    placed    inside    this 
hollow  cylinder,  thereby  becoming  magnet- 
ised as  soon  as  the  current  is  switched  on  in 
the    primary    circuit,    and   thus    creating   a 
field  of  force  of  its  own. 

(3)  The  secondary  is  made  of  great  length 
(being  wound  around  the  primary  many  thou- 
sands of  times)  and  of  very  high  resistance. 

(4)  The  magnetic  field  created  by  the  cur- 
rent passing  through  the  primary  winding  is 
rapidly  destroyed  and  remade.    This  is  done 
by  closing  and  reopening  the  primary  circuit. 

It  must  be  borne  in  mind  that  the  current 
induced  in  the  secondary  circuit  will  produce 
a  detrimental  effect  on  that  flowing  through 
the  primary.  It  does,  in  fact,  tend  to  stop 
the  primary  voltage  rising  instantaneously  to 
its  full  pressure  when  the  current  is  switched 
on.  This  check  to  the  instantaneous  rise  in 
voltage  on  the  primary  winding  reacts  again 
on  the  secondary. 

Similarly,  when  the  current  hi  the  primary 


138  THE  FLYER'S  GUIDE 

circuit  is  switched  off,  that  set  up  in  the 
secondary  will  still  tend  to  keep  it  moving 
on  in  the  same  direction. 

To  overcome  this  effect  of  reinduction  from 
the  secondary  back  to  the  primary  circuit, 
a  condenser  is  fitted  to  the  latter.  A  con- 
denser is  formed  of  a  number  of  sheets  of 
tin  foil  insulated  from  each  other  by  oiled 
paper,  and  has  the  effect  of  rapidly  reversing 
the  current  in  its  circuit  (primary). 

The  simplest  form  of  electric  ignition  is 
worked  by  an  accumulator  and  trembler  coil. 
Diagram  T  is  a  diagrammatic  representation 
of  this  form  ijpr  a  single  cylinder  engine,  and 
should  be  studied  in  conjunction  with  the 
following  explanation. 

One  terminal  of  the  accumulator  (it  does 
not  make  the  slightest  difference  whether  this 
is  the  positive  or  negative  terminal)  is  led 
to  earth  (the  bedplate  of  the  engine  for  con- 
venience). The  other  terminal  is  led  to  the 
adjustable  screw  on  the  trembler.  The  trem- 
bler blade  when  in  its  normal  position  is  so 
adjusted  as  to  make  contact  with  the  adjust- 
able screw.  Both  the  point  of  the  screw 


Primary  Circuit 
Secondary  C/rcu/'t 


DIAGRAM  T.  —  IGNITING  ARRANGEMENT  FOR  SINGLE-CYLINDER 
ENGINE  (ACCUMULATOR  AND  TREMBLER  COIL). 


IGNITION  DEVICES  139 

and  the  point  of  contact  of  the  blade  should 
be  platinum  (other  metals  are  burnt  away 
by  the  spark  produced  on  contact  being 
broken). 

The  trembler  blade  is  connected  at  one 
end  of  the  primary  winding  of  the  induction 
coil  (otherwise  the  blade  is  insulated).  This 
blade  is  made  of  spring  steel,  and  is  kept 
in  position  at  only  one  end  by  a  single  screw. 
The  other  end,  to  which  a  piece  of  soft 
iron  is  fixed,  covers  the  core  of  the  induc- 
tion coil.  In  its  normal  position  the  end  of 
the  trembler  blade  does  not  touch  the  core 
of  the  coil,  but  is  about  -£$  inch  from  it. 
The  core  consists  of  a  bundle  of  soft  iron 
wires  around  which  the  primary  coil  is  wound. 
The  latter  consists  of  about  twenty  feet  of 
thick  insulated  wire,  the  other  end  of  which 
is  connected  to  the  brush  of  a  wipe  con- 
tact. This  brush  (carbon)  bears  on  the  per- 
imeter of  a  fibre  (or  any  non-conducting) 
disc  which  is  revolving  at  half  the  speed 
of  the  crankshaft  (it  is  usually  mounted  on 
the  camshaft).  This  disc  has  let  into  it  a 
brass  (or  any  good  conducting  metal)  seg- 


140  THE  FLYER'S  GUIDE 

ment,  which  is  earthed  through  the  spindle 
of  the  shaft.  The  disc  has  to  be  so  timed 
that  the  segment  and  brush  are  in  contact 
when  it  is  required  to  fire  the  charge  in 
the  cylinder.  The  secondary  winding  is  made 
up  of  about  one  and  a  half  miles  of  wire 
of  very  thin  diameter  coiled  round  over  the 
primary.  One  end  of  the  secondary  winding 
is  earthed,  the  other  being  led  to  the  central 
electrode  of  the  sparking  plug.  As  soon  as 
the  brush  comes  into  contact  with  the  metal 
segment  of  the  wipe  contact  the  primary 
circuit  becomes  closed. 

There  are  two  instantaneous  effects  of  this 
closing  of  the  primary  circuit. 

(a)  An  induced  current  is  set  up  in  the 
secondary  winding. 

(6)  The  soft  iron  core  becomes  magnetised. 
The  effect  of  this  is  to  draw  the  trembler 
blade  down  on  to  the  core.  As  soon  as  this 
happens  the  adjustable  screw  ceases  to  touch 
the  blade,  and  the  circuit  is  therefore  broken 
— that  is,  the  primary  circuit  is  no  longer 
closed  and  the  core  of  the  coil  becomes  de- 
magnetised, thus  releasing  the  trembler  blade 


IGNITION  DEVICES  141 

which  springs  back  into  its  normal  position 
and  again  makes  contact  with  the  adjustable 
screw. 

This  making  and  breaking  of  the  primary 
circuit  is  instantaneous,  and  occurs  during 
the  whole  time  the  brush  on  the  commutator 
is  in  contact  with  the  metal  segment. 

Every  time  the  primary  circuit  is  thus 
made  and  broken  an  induced  current  of  very 
high  voltage  is  created  in  the  secondary 
winding.  As  already  explained,  one  end  of 
the  secondary  winding  is  earthed,  while  the 
other  is  led  to  the  central  electrode  of  the 
sparking  plug  and  so  insulated.  The  only 
path  available  for  the  secondary  current  is 
across  the  points  of  the  sparking  plug,  which 
distance  is  jumped  and  a  spark  created 
thereby. 

The  necessity  for  a  condenser  to  ensure 
the  rapid  reversal  of  the  primary  current 
on  contact  being  broken  has  already  been 
alluded  to.  The  condenser  is  connected  in 
parallel  with  the  make  and  break  (that  is, 
the  trembler  blade  and  screw),  and  performs 
the  function  of  Ley  den  jar  or  storage  battery. 


142  THE  FLYER'S  GUIDE 

The  condenser  accommodates  the  current  so 
rapidly  that  it  becomes  overcharged  and  dis- 
charges its  current  again,  causing  a  flow  in 
the  opposite  direction. 

The  same  principle  is  of  course  applicable 
to  a  multi-cylinder  engine.  For  example, 
take  a  four-cylinder  engine. 

There  are  two  ways  of  doing  it: 

(a)  By  using  four  separate  induction  coils; 

(b)  By  using  only  one  coil  and  a  distributor. 

(a)  The  general  principle  is  identical  to  the 
above.     As   four   coils   are  being   employed 
there   would,    of    course,    have   to   be   four 
brushes   on   the    commutator    (or   else   four 
earth  segments  on  the  disc  and  one  brush). 
One  end  of  the  secondary  winding  on  each 
coil  would  lead   to   its  respective  sparking 
plug,  the  other  being  earthed  as  before. 

(b)  This  case  is  represented  in  diagram  U. 

The  commutator  has  four  earthed  seg- 
ments, and  is  timed  so  that  one  segment  is 
in  contact,  with  the  brush  when  each  cylinder 
should  be  firing.  The  primary  circuit  is  iden- 
tical to  that  illustrated  in  diagram  T. 


Commutator 


DIAGRAM  U. — IGNITION  ARRANGEMENTS  FOR  FOUR-CYLINDER 
ENGINE,  ACCUMULATOR,  AND  ONE  TREMBLER  COIL. 


IGNITION  DEVICES  143 

One  end  of  the  secondary  circuit  is  earthed, 
the  other  being  led  to  the  revolving  arm  of 
the  distributor.  In  practice  both  the  dis- 
tributor and  commutator  would  be  mounted 
on  one  shaft  (usually  the  camshaft — anyway, 
it  must  be  a  half-time  shaft),  although  this 
cannot  be  represented  diagrammatically.  The 
revolving  part  of  the  distributor  is  insulated, 
and,  as  it  goes  round,  it  rubs  against  the 
inside  of  a  fibre  (or  vulcanite)  ring.  Four 
metal  strips  are  let  into  this  ring,  from  which 
four  high  tension  wires  lead  to  the  sparking 
plug.  As  the  revolving  parts  of  the  distributor 
touch  the  metal  strip,  the  secondary  circuit 
becomes  closed  so  that  its  current  can  pass 
from  the  coil  to  the  sparking  plug.  The 
distributor  must,  of  course,  be  accurately 
timed. 

In  all  the  above  cases  a  considerable  varia- 
tion can  be  given  to  the  time  at  which  the 
spark  occurs  by  moving  the  position  of  the 
brush  on  the  commutator.  Arrangements  are 
usually  made  for  this  to  be  done  from  the 
driver's  or  pilot's  seat.  In  the  last  case 
it  can  also  be  done  by  giving  a  slight  move- 


144  THE  FLYER'S  GUIDE 

merit  to  the  nonrevolving  part  of  the  dis- 
tributor. 

In  all  the  above  cases  an  ordinary  switch 
can  be  fitted  to  the  primary  circuit.  When 
the  switch  is  off  (i.e.  open)  there  is  no  path 
for  the  primary  circuit;  consequently  there 
can  be  no  induced  current  in  the  secondary. 

In  practice,  of  course,  magnetos  are  al- 
most exclusively  used  so  as  to  avoid  carrying 
accumulators  or  dry  cells,  which  always  run 
down  after  a  certain  amount  of  use. 

The  magneto  works  on  the  same  prin- 
ciples as  the  above,  except  that  the  primary 
current  is  generated  by  a  dynamo^  the  make 
and  break  being  mechanical. 

The  principle  of  the  magneto  is  briefly  as 
under: 

A  powerful  steel  horse-shoe  magneto  is 
fitted  with  soft  iron  pole-shoes.,  (Diagram 
V  shows  this  in  elevation.)  An  armature, 
mounted  on  a  steel  spindle,  and  composed 
of  a  laminated  shuttle-core  of  soft  iron,  about 
which  the  primary  wiring  is  wound,  revolves 
inside  the  pole-shoes. 

As  before,  the  primary  winding  consists  of 


IGNITION  DEVICES 


145 


about  twenty  feet  of  thick  (low-resistance) 
insulated  wire,  one  end  of  which  is  anchored 
to  the  armature  and  so  earthed,  whilst  the 


_  Permanent 
Stee/Magrtet 


-Soft    /ron 


DIAGRAM  V. — SECTION  SHOWING  PERMANENT  MAGNET, 
ARMATURE  AND  POLE-SHOES. 

other  is  connected  to  the  fixed  end  of  the 
contact  breaker,  through  a  long  fastening 
screw,  which  is  insulated  from  the  armature. 


146  THE  FLYER'S  GUIDE 

The  contact  breaker  is  mounted  on  a  disc 
of  non-conducting  material  (usually  fibre), 
which  is  mounted  on  and  revolves  with  the 
spindle.  A  brass  lug  is  mounted  on  this 
insulated  disc  and  kept  in  place  by  the 
fastening  screw,  which  passes  through  the 
centre  of  each.  A  platinum-tipped  screw  pass- 
ing through  this  lug  forms  the  fixed  part  of 
the  contact  breaker,  the  moving  portion  of 
which  is  provided  by  a  bell  crank  lever 
also  mounted  on  the  fibre  disc.  One  end  of 
this  lever  has  a  platinum-tipped  screw  pass- 
ing through  it,  while  the  other  is  fitted  with 
a  small  roller.  This  bell  crank  lever  is  pivoted 
about  its  elbow,  as  shown  in  diagram  W,  and 
is  kept  in  position  by  a  light  spring,  so  that 
its  platinum-tipped  screw  is  in  contact  with 
that  on  the  fixed  portion  of  the  make  and 
break. 

The  pivoting  point  is  earthed  by  means 
of  a  flat  spring,  which  also  serves  to  keep  the 
whole  lever  in  place.  One  end  of  this  spring 
presses  down  on  the  pivoting  point;  the  other 
is  connected  to  a  carbon  brush,  which  is  let 
into  the  inside  face  of  insulated  disc,  and 


r/yn 
Tens/on 
/ead  to 
Distributor 


Switch 


Co/fecting 


(/nsu/ated  from  Sp/nd/e) 

Secondary  Circuit 
Primary  C/rcvt't-~ 


DIAGRAM  W. 

a  =  steel  spring:  bears  on  fastening  screw  K;  makes  earth  when  switch 
is  closed.  6  =  bell  crank  lever  of  make  and  break.  c  =  fixed  part 
of  make  and  break,  di  and  da  =  projections  on  fixed  part  of  machine. 
H  =  spring  keeping  bell  crank  lever  down.  K  =  fastening  screw. 
J  =  small  spiral  spring  keeping  bell  crank  lever  in  such  position  that 
the  points  of  make  and  break  (Sc  and  Sc)  are  touching  (except  when 
displaced  by  the  projections  d\  and  &) .  L  =  screw  at  fulcrum  of 
bell  crank  lever,  x  =  carbon  brush  earthing  bell  crank  lever. 


IGNITION  DEVICES  147 

presses  against  the  framework  of  the  mag- 
neto throughout  its  circular  track. 

When  the  magneto  is  being  turned,  the 
roller  on  one  end  of  the  bell  crank  lever  (de- 
scribed above)  travels  in  a  circular  path. 
Two  projections  are  fitted  in  this  path.  As 
the  end  of  the  bell  crank  lever  hits  these 
.projections,  the  lever  is  bound  to  turn  around 
its  own  pivot,  thus  forcing  the  two  portions 
of  the  contact  breaker  apart.  As  soon  as 
the  projection  is  passed,  the  spring  on  the 
lever  pulls  the  latter  back  into  its  normal 
position,  thus  remaking  contact.  (This  ex- 
planation should  be  read  in  conjunction  with 
diagram  W.) 

A  condenser,  mounted  on  the  spindle,  is 
wired  in  parallel  with  the  contact  breaker 
(exactly  as  with  the  accumulator  and  coil 
ignition). 

The  secondary  winding,  as  in  the  case  of 
the  ordinary  induction  coil,  consists  of  about 
one  and  a  half  miles  of  wire  of  very  small 
diameter  wound  over  the  primary.  One  end 
of  this  is  earthed  (in  practice  it  is  anchored 
to  the  spindle  with  the  earthed  end  of  the 


148  THE  FLYER'S  GUIDE 

primary  winding),  the  other  end  being  con- 
nected to  a  slip  ring,  which  is  mounted  on, 
but  insulated  from,  the  spindle. 

A  carbon  brush  bearing  on  the  slip  ring 
(or  collecting  ring)  conveys  the  secondary  cur- 
rent to  the  distributor,  whence  it  is  led  to  the 
sparking  plugs  as  described  above. 

The  lead  from  the  carbon  brush  to  the  dis- 
tributor is  in  parallel  with  a  safety  spark  gap. 
The  safety  spark  gap  is  similar  to  a  spark- 
ing plug,  but  with  an  appreciably  larger  gap. 
The  gap  must  be  sufficiently  large  to  ensure 
that  the  resistance  offered  to  jumping  the 
spark  gap  (which  is  only  under  atmospheric 
pressure)  is  greater  than  that  offered  by  jump- 
ing the  gap  of  the  sparking  plug  (which  is 
under  high  pressure).  The  spark  gap  will 
not  therefore  normally  come  unto  use.  Should 
the  high  tension  leads  come  undone  or  be  broken 
(or  sparking  plug  break,  etc.),  the  high  ten- 
sion current  would  then  have  a  path  to  earth 
across  the  safety  gap. 

If  this  outlet  to  earth  were  not  available, 
the  current,  being  of  so  high  a  voltage,  would 
probably  burn  out  the  insulation. 


IGNITION  DEVICES  149 

To  sum  up,  then,  the  action  is  as  follows: 

A  spindle  carrying  soft  iron  armature,  pri- 
mary winding  and  secondary  winding  re- 
volves hi  a  magnetic  field.  As  the  lines  of 
force  are  broken,  a  low  tension  current  is  set 
up  hi  the  primary  winding.  This  current  is 
instantaneously  broken  by  the  mechanical 
make  and  break. 

The  making  and  breaking  of  this  primary 
circuit,  intensified  by  the  action  of  the  con- 
denser, induces  a  very  high  voltage  current 
in  the  secondary  circuit. 

The  secondary  circuit  is  led  off  from  the 
collecting  ring  through  a  carbon  brush  to 
the  distributor,  thence  across  the  plugs  to 
earth. 

The  moment  when  the  highest  current  is 
set  up  in  the  primary  circuit  is  that  at  which 
the  armature  just  breaks  the  lines  of  force 
of  the  permanent  magnetic  field  (position 
shown  in  diagram  X).  Such  a  position  then 
occurs  twice  in  one  revolution  of  the  armature. 

The  actual  break  of  the  primary  circuit 
must  then  be  timed  to  occur  when  the  arma- 
ture is  in  such  a  position. 


150  THE  FLYER'S  GUIDE 

Now  a  single-cylinder  engine  only  requires 
one  spark  in  every  two  revolutions  of  the 
crankshaft — that  is  to  say,  the  magneto  could 
be  mounted  on  the  camshaft,  provided  there 
was  only  one  break  per  revolution  of  the 
armature  (in  the  foregoing  description  of  a 


DIAGRAM  X. 

make  and  break  it  was  assumed  to  break 
twice  per  armature  revolution;  it  can  just 
as  easily  be  made  to  break  only  once  per 
revolution).  The  break  would  have  to  be 
correctly  timed  so  as  to  occur  about  25° 
before  top  dead  centre  of  the  crank.  The 
high  tension  lead  could  then  be  led  direct 
from  the  brush  of  the  collecting  ring  to  the 
sparking  plug  without  passing  through  a  dis- 
tributor. 


IGNITION  DEVICES  151 

In  the  case  of  a  two-cylinder  engine  the 
magneto  (with  two  breaks  per  revolution  of 
the  armature  as  originally  described)  should 
be  mounted  on  the  camshaft.  Two  sparks 
are  then  obtained  per  one  revolution  of  the 
camshaft.  That  is  equivalent  to  one  per 
revolution  of  the  crankshaft,  which  is  what 
is  required  for  a  two-cylinder  engine.  In  this 
case  the  high  tension  circuit  would  have  to  be 
led  through  a  distributor  to  each  plug. 

In  the  case  of  a  four-cylinder  engine  the 
armature  would  have  to  be  revolving  at  the 
same  speed  as  the  crankshaft. 

In  a  seven-cylinder  engine  (e.g.  Gnome) 
it  would  have  to  be  geared  as  7  to  4  with 
reference  to  the  crankshaft  and  so  on. 

In  each  case,  of  course,  the  distributor  must 
be  timed  correctly  in  conjunction  with  the 
make  and  break. 

Owing  to  the  fact  that  the  whole  of  the 
primary  winding  is  revolving,  it  cannot  be 
provided  with  a  switch  (as  in  the  case  of 
accumulator  ignition).  Therefore,  another 
means  of  switching  off  has  to  be  devised. 

As  already  explained,  the  high  voltage  cur- 


152  THE  FLYER'S  GUIDE 

rent  induced  in  the  secondary  winding  is 
dependent  on  the  make  and  break  of  the 
primary  circuit.  If,  therefore,  the  make  and 
break  is  cut  out,  no  high  voltage  current  will 
be  set  up  in  the  secondary  circuit. 

This  is  done  by  providing  a  direct  path  to 
earth  for  the  primary  current,  so  that  when 
the  make  and  break  opens,  the  circuit  is  not 
really  broken. 

In  practice  a  flat  steel  spring  bears  on  the 
top  of  the  fastening  screw  (see  diagram  W). 
The  other  end  of  the  spring  is  fixed  to, 
but  insulated  from,  the  fixed  part  of  the 
magneto.  A  lead  from  this  spring  is  then 
connected  to  one  terminal  of  a  tumbler 
switch,  the  other  terminal  of  which  is  con- 
nected to  earth. 

When  the  switch  is  open,  the  current  has  no 
path  to  earth,  and  the  make  and  break  is 
therefore  not  short-circuited.  Consequently, 
a  secondary  current  is  produced  and  led  to 
the  plugs.  That  is  the  position  known  as 
"Contact." 

On  the  other  hand,  when  the  switch  is 
closed,  the  make  and  break  is  short-circuited 


IGNITION  DEVICES  153 

and  no  secondary  current  is  produced.  That 
is  the  position  known  as  "  Switch  off." 

As  these  positions  of  the  switch  are  con- 
trary to  the  ordinary  acceptance  of  the 
terms  "  switch  off"  and  "  contact,"  great  care 
must  be  taken  to  see  that  switches  are  marked 
correctly. 

One  cannot  emphasise  this  point  too 
strongly,  especially  where  inexperienced  me- 
chanics are  concerned.  A  switch  incorrectly 
marked  may  have  fatal  results  where  pro- 
peller swinging  is  involved. 


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